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COPYRIGHT DEPOSITS 



Geography 

Grade 8 A 
Mathematical and Physical 



By 

Harmon B. Niver 




I 



_ ESE-qjWIVTCW _ 



I9I2 

ATKINSON, MENTZER & COMPANY 
CHICAGO NEW YORK DALLAS BOSTON 



4' 



Copyright, 1912 

BY 

HARMON B. NIVER 



Writ UafefstlJE ^rtsa 

R. R. DONNELLEY & SONS COMPANY 
CHICAGO 



^CI.A317040 



PREFACE 

The following brief treatise on the elements of math- 
ematical and physical geography has been prepared to 
meet the requirements of elementary schools. Much of 
the material here given has already been taken up at 
intervals during the regular geographical course. Enough 
new matter has been added to provide for a term's work 
on these subjects. A number of astronomical facts have 
been given in the first chapter, not strictly related to geog- 
raphy but such as everyone ought to know. Chapters V 
and VI, dealing with the magnetism of the earth, the 
moon's phases, and eclipses, are also not defensible as 
geography, but are introduced as matters of general infor- 
mation. The remaining chapters of the book treat of the 
general features of the earth, of the forces at work in alter- 
ing its surface, and of atmospheric and oceanic movements. 
The final chapters deal with the distribution of plant and 
animal life and with the races of man and their physical 
and social characteristics. It is believed that the book 
can be used as the basis for a half-year of profitable work at 
the close of the elementary school course. 



CONTENTS 

Chapter Page 

I. The Earth as a Planet i 

II. Form and Size of the Earth ii 

III. The Earth's Motions and their Effects . 14 

IV. Time and Distance on the Earth ... 20 
V. The Earth's Magnetism 26 

VI. Phases of the Moon — Eclipses .... 30 

VII. General Features of the Earth ... 34 

VIII. Mountains and Plateaus 44 

IX. Earthquakes and Volcanoes 52 

X. Erosion and Glaciation . 59 

XI. The Waters of the Land 72 

XII. Islands 79 

XIII. The Coast Line 84 

XIV. The Sea 88 

XV. The Atmosphere 99 

XVI. Temperature and Pressure 107 

XVII. Winds, Rains, and Storms 11 1 

XVIII. Weather and Climate . 124 

XIX. Plant Life '.131 

XX. Animal Life 140 

XXI. Man 154 



GEOGRAPHY 

MATHEMATICAL AND 

PHYSICAL 



CHAPTER I 

THE EARTH AS A PLANET 

Fixed Stars and Planets. We have learned that the 
earth is a great round ball composed of land, water, and 
air, and that it is traveling rapidly onward in its never- 
ending journey around the sun. But perhaps we have 
never thought of the earth as having any likeness to the 
stars which we see in the skies on a clear night. It is hard 
to believe that it is really one of that company of glitter- 
ing lights that flash and twinkle in the far off depths of 
space. 

If we observe the stars carefully night after night, we 
shall become familiar with the constellations, or star- 
groups, which were observed and named by astronomers 
thousands of years ago. Most of us can recognize the 
Great Bear, or Dipper, the v-shaped Hyades, and the 
Pleiades, or Seven Sisters, above them. Orion with 
the three stars in his belt, the Twins, Sirius, the Dog-Star, 
the brightest in the sky, Hercules, Polaris, or the North 
Star, are other constellations and stars with which we 
should become acquainted. With the eye alone we can 



PHYSICAL GEOGRAPHY 



see only a few thousand stars; but when a telescope is used, 
millions of others are brought into view. 

Nearly all of the stars that we can see are fixed stars. 

They occupy to- 
day nearly the 
same positions 
in the skies as 
when man first 
beheld them. 
Other stars 
change their 
positions from 
night to night, 
until after a 
certain time 
they return to 
the positions 
where they were 
first observed. 
There are seven 
principal stars of 
this class which we may observe from the earth. They are 
called planets, a word meaning wanderers. The earth also is 
a planet, and if we could see it from a great distance, as we 
see the other planets, it would appear to us like one of them. 

The planets have been named after the Greek and Roman gods. 
Nearest the sun is Mercury, named for the messenger of the gods because 
of his swiftness. Next is Venus, the brightest of the planets, named 
after the goddess of beauty. Beyond the earth is Mars, which received 
the name of the war-god on account of its red color. Next is Jupiter, 
the largest planet, and hence named after the king of the gods. Most 
distant from the sun are Saturn, Uranus, and Neptune. Between 
Mars and Jupiter are several hundred smaller planets called asteroids. 
These and Neptune cannot be seen without a telescope. 




Fig. I. 
North star, 



Some nf the constellations surrounding the 



THE EARTH AS A PLANET 



The planets revolve about the sun, but at different 
distances from it. The nearer a planet is to the sun, the 
faster it moves. Our earth makes one complete revolution 
in 365M days. This period we call a year. Mercury, the 
planet nearest the sun, makes the journey in 87 days. 
Mercury's year, therefore, is only about one fourth as long 
as ours. Neptune, the most 
distant planet, is 30 times as 
far away from the sun as the 
earth. He travels only one /asteroids mRs vemus 

sixth as fast as the earth, and / earth me:rcur/\ 

requires 165 years as long as 

ours to make one journey Ineptume saturm 

around the sun. 

The following table shows \ ^^^^^ ^^^^^ 

the chief numerical facts about 
the eight greater planets ap- 
proximately correct in round pig. 2. Showing the relative sizes of 

numbers. *^^ p^^^^^'- 

Y)- ^ ■ Average distance Time of Rev- Velocity in 
Name -i from the sun in olution miles per 

millions of miles in days second 

Mercury 3,ooo 36 87 29 

Venus 7j700 67 225 22 

Earth 7,918 92 365 18 

Mars 4,200 141 687 15 

Jupiter 86,000 483 4,333 8 

Saturn 73,ooo 886 10,759 6 

Uranus. 32,000 1,800 30,687 4 

Neptune 3S,ooo 2,800 60,181 3 

The laws governing the motions of the planets were 
discovered by Johann Kepler, a German astronomer, in 
the early part of the 17th century. The first law is stated 
as follows: The orbit of each planet is an ellipse with the 
sun as one of its foci. 




PHYSICAL GEOGRAPHY 



The method of drawing an ellipse is shown in Fig. 3. A loop of cord 
is passed around two pins driven into a piece of cardboard. The point 

of a pencil is then inserted 
in the loop, and, keeping the 
string stretched taut, the 
ellipse is described about 
the pins in the manner in- 
dicated. The points marked 
by the pins are the foci. 
If the distance between the 
pins be made less, or if the 
cord be lengthened, the form 
of the ellipse will more 
nearly approach a circle 
and the major axis and the 
minor axis (Fig. 4.) will be 
more nearly equal. The 
deviation of an ellipse from 
the circular form is called 
its "eccentricity" and de- 
pends upon the distance be- 
tween the foci. 




Fig. 3. Method of drawing an ellipse. A and 
B are the foci, CD the major axis, and EF the 
minor axis. 



The orbits of the plan- 
ets are nearly circular, as 
in Fig. 4. A planet when 
crossing the major axis 
at one of its extremi- 
ties is at its greatest dis- 
tance from the sun. This 
position is called its 
aphelion; when crossing 
the major axis at its other 
extremity it is in perihe- 
lion; that is, the position 
nearest the sun. The other 
laws of planetary motion 
are too difficult to be con- 
sidered here. 




Fig. 4. An ellipse with very slight eccen- 
tricity resembling the orbits of the planets. 



THE EARTH AS A PLANET 



Moons. All the planets, except Mercury and Venus, 
have bodies revolving about them called moons, or satellites. 
We have all seen the new moon as a slender crescent in the 
west just after sunset. If vv-e observe it for several nights 
at the same hour, we may notice that it is farther and farther 
above the horizon and that it appears to have moved 
toward the east. At the end of two weeks we may see it 
just after sunset as the full moon, near the eastern horizon; 
it has now moved all the way across the sky. Two weeks 
later it appears again in the west, having revolved entirely 
about the earth from west to east. All the moons revolve 
about their planets, and all the planets revolve about the 
sun in the same direction. With a telescope, or even with a 
good field-glass, we may watch the moons of Jupiter revolv- 
ing about that planet. We may also watch the revolution 
of the planets about the sun, only these observations must 
be far more exact. 



Comets and Mete- 
ors are strange, fiery 
bodies that occasion- 
ally appear in the 
heavens, and pass 
out of sight as mys- 
teriously as they 
come. The comets 
circle about the sun, 
and then dart away 
on some unknown 
path into distant 
parts of the universe, 
sometimes reappear- 
ing after many years. 



PATH OF 

MALLEY*5 

COME.T 




?■ 5 



A part of the path of Halle/'s comet, 
showing its progress around the sun, and its distance 
from the earth at different times. 



PHYSICAL GEOGRAPHY 



Meteors, or "shooting" stars, flash suddenly through the 

earth's atmosphere, some turning to vapor and others 

faUing upon its surface. 

One of the most remarkable comets whose period of revolution about 
the sun is known is that named after Edmund Halley, who predicted 
its appearance in 1759. This comet enters the solar system and passes 
about the sun every seventy-five years. It was first seen before the 
Christian Era. It was noticed again in 684, 1066, 1456, 1682, 1759, and 
1835. Its last appearance was in 1910. A portion of its path about 
the sun is shown in Fig. 5. 

The Solar System is a name given to the sun and all the 
planets with their moons that revolve about it. The sun 
is the center of the solar system. It is thought to be a 
white hot mass of matter enveloped in burning vapors. 
Great flames leap from its surface to a height of over 
200,000 miles, a distance nearly as great as that from the 
earth to the moon. The diameter of the sun is 866,500 
miles, or about one hundred times that of the earth. Its 
volume is 1,300,000 times as great as that of the earth and 
its average distance from the earth is about 93,000,000 
miles. The sun supplies the earth with the light and 
heat necessary to support plant and animal life. 

The sun is really one of the fixed stars and the one nearest to us. 
Like the planets, it rotates about its axis. By means of the dark spots 
which sometimes appear upon its surface, its period of rotation has been 
found to be about 25 days. The amount of heat given out by the sun 
is so great as to be beyond computation. The earth alone receives 
enough heat in one year to melt a layer of ice 137 feet thick and covering 
its entire surface, yet the amount of heat received by the earth is only 
■2.T0 o.oV o.oTo P^rt of the total heat given out by the sun. 

The revolution of the planets about the sun was dis- 
covered about four centuries ago by a German astronomer 
named Copernicus. He showed also that day and night 
are caused by the rotation of the planets upon their axes. 
The sun rotates on its axis like a planet, and with all its 



THE EARTH AS A PLANET 




URAMUS 




attending planets and their moons is moving slowly through 
space. The fixed stars are fiery suns like our own. Per- 
haps they, too, are centers of systems of planets; but they 
are so far away that even with our largest telescopes we 
can find out little about them. 

The Nebular Theory. It is thought that the sun and 
all the planets were 



once one great 
mass of fiery va- 
por, filling all the 
space between the 
sun and the far- 
thest planet. We 
do not know where 
this cloudy mass 
came from. But 
after a time it be- 
gan to cool, and 
as it grew smaller, 
began to rotate 
slowly about its 
axis, just as the 
earth does now. 
This motion 
caused it to bulge 
out at the equator 
and flatten at the 
poles. The motion 
at the equator be- 
came so rapid that 
a number of rings 
of vaporous matter 




Fig. 6. The planets and their orbits, showing rela- 
tive distances from the sun. 



PHYSICAL GEOGRAPHY 



were thrown off. Tliese rings in some- way gradually became 
spheres and continued to revolve as planets about the 
central mass, or sun. Some of the planets themselves threw 
off rings which formed into moons. 

The planets were once white hot, as the sun is now; but 
as they cooled at the surface, a hard crust formed, which 
grew thicker and thicker as the cooling continued. But 
how did this crust, which must have been smooth at first, 
become so rough and irregular.^ When melted rock cools 
it becomes about one seventh of its volume smaller; accord- 
ingly, as the hot rock within the crust went on cooling, it 
kept shrinking, and contracting. The crust, on account of 
its weight, pressed toward the center, and crumpled here 
and there in broad folds, like a garment that does not fit, 
or like a carpet that is too large for a floor. 

The earth has been compared to an apple that has been baked. 
The heat makes the apple expand until the skin is almost bursting, but 
when the apple cools it shrinks until the skin becomes too large and 
lies in folds, or wrinkles. The upward folds formed by the cooling of 
the earth grew into the continents, while into the downward folds 
poured the waters that had been condensed from the clouds of 

steam surrounding the earth. 

There are several reasons for believing 

\ this theory. First, the motions of the 

sun, the planets, and their moons are all 

in the same direction. Second, the planet 

Saturn has still two rings circling about 

• ■';■.' \y>. it. Again, the planet Jupiter is still so 

-;;.".';-',''. hot that its atmosphere is filled with clouds 

_-,.•'.•'• of steam. That the interior of our earth 

ii^?-fe^"s"'':"' ^^ highly heated is shown by hot springs 

tV,**li3?r..- • and volcanoes which break through its 

■^mi^ -'^ surface. That the moon was once in a 

"^'f heated condition is evident from the dead 

volcanoes still visible upon it. We believe 

that the sun is still cooling and contracting; 

Fig. 7. Photoiraph of a ^^^ perhaps it may yet throw off rings of 

baked apple. matter to be formed into planets. It is 



THE EARTH AS A PLANET 



thought, also, that the earth, the planets, and the sun itself will some 
day grow cold like our moon, and that all life upon the earth will cease. 

Gravitation. The members of the solar system as well 
as all the distant stars are held in their places by a force 
called gravitation; their motions also and the paths they 
follow are effects of the same force. 

The law of gravitatioii as stated by Sir Isaac Newton, 
who discovered it, is as follows: 

Every particle of matter in the universe attracts every 
other particle of matter, with a force which varies directly as 
the masses of the particles, and inversely as the square of the 
distance between them. 

Gravitation is thus a form of attraction that tends to draw 
bodies of matter together. We do not understand the 
cause of it any more than we understand why a magnet 
attracts a piece of steel or iron. From the first part of the 
law it follows that if the amount of matter that two bodies 
contain should be doubled, the attractive force between 
them would be doubled. The second part of the law means 
that if the bodies should be twice as far apart, the attraction 
would be only one fourth as great; if the distance be three 
times as great then the attraction between them will be 
only one ninth as great. On the contrary, if the distance 
be divided by two, the attraction will be multiplied by four, 
etc. It is the force of gravitation which causes bodies to 
fall to the earth and which gives them weight. It is said 
that Newton's attention was first drawn to this subject 
by seeing an apple fall to the earth. 

The onward motion of the planets causes a force, which 
tends to draw them away from the sun. This force is 
known as inertia, or centrifugal force. But the attraction 
between a planet and the sun (gravitation) is exactly equal 



lo PHYSICAL GEOGRAPHY 

to the centrifugal force, and thus the planets are held in 

their courses. 

A familiar illustration of the two forces named above is furnished 
by tying a string to a body and whirling it about in a circle. The 
tendency of the body to fly ofi' in a straight line is the force of inertia, 
while the pull on the string may represent gravitation. These two 
forces are always equal. It may be added that if the speed of the body 
be increased the pull on the string will be correspondingly greater, and 
vice versa. This illustrates why the planets nearer the sun revolve 
more swiftly than those that are more remote. 

REVIEW. I. Describe some of the leading constellations. 2. Which one is useful 
in determining direction? 3. How may we distinguish planets and fixed stars? 4. Name 
the eight principal planets. 5. How is the motion of the planet affected by its distance 
from the sun? 6. Compare the year of Mercury with that of the earth. Compare also 
the year of Neptune. 7. What is the first law of planetary motion? 8. Describe the 
method of drawing an ellipse. 9. What is meant by aphelion and perihelion? 10. Which 
of the planets have moons? 11. Describe the changes in the appearance of the moon. 
12. Comets and meteors. 13. What is meant by the Solar System? 14. Describe the 
sun and the amount of heat that it gives out. 15. Who was Copernicus? 16. Write 
a paragraph about the Nebular Theory. 17. State the law of gravitation. 18. What 
is meant by inertia? 



CHAPTER II 




Fig. 8. In traveling from A toward 
B and C new stars appear to rise at N 
andO. 



FORM AND SIZE OF THE EARTH 

The shape of the earth as well as that of the other planets 
and heavenly bodies is spherical or nearly so. This fact 
is easily established in the case of the other planets by 
direct observation; but it is 
not so easy to prove the shape 
of the earth, because so little 
of it can be seen at one time. 
By scientific methods, how- 
ever a number of proofs have 
been accumulated, which 
show conclusively that the 
earth is spherical. The first of these that we shall mention 
was observed by travelers more than 2,000 years ago. To 
one who travels north or south, new stars are constantly 
coming into view, while the stars behind disappear below 

the horizon. To an observer 
at the equator, the North star 
appears to be on the horizon. 
But as one travels north it 
gradually rises, until on reach- 
ing the pole it would appear 
directly overhead. 

The well-known fact also 
that the sun rises earlier at 
places east of us and later at 




Fig. 9. The horizon seen from differ- 
ent elevations. 



places west of us shows that 



12 



PHYSICAL GEOGRAPHY 



the surface of the earth is curved; for if it were flat the sun 
would rise and set at the same time for all places on the 
earth. There would also be no apparent rising and setting 

of the stars to a traveler 
going either north or south. 
Another proof is the shape of 
the earth's shadow as seen 
upon the moon at the time of 
an eclipse of the moon. This 
shadow is always circular, no 
matter what the position of 
the earth may be, and only a 
sphere always casts a circular 
shadow. Among the more 
familiar pr.oofs of the earth's 
spherical shape is the circular 
appearance of the horizon when viewed from a great eleva- 
tion. When ships are coming into port or sailing away, 
the tops of the masts are the first seen and the last to 
fade out of sight; whereas, if the surface of the earth were 
flat, the hull, being the most conspicuous part of a ship. 




Fig. 10. 
the moon. 



The earth's shadow upon 





Fig. II. An orange and lemon, illustrating spheroidal forms. 



FORM AND SIZE OF THE EARTH 



13 



would be seen first. The circumnavigation of the earth is 
another familiar proof of its form. This, however, is not 
conclusive, as it must always be accomplished in an east 
and west direction, which would be 
possible if the earth were a cylinder. 
Finally, from analogy with the other 
members of the solar system, we 
might reasonably conclude that the 
earth is spherical. 




Fig. 12. Illustrating the 
effect of rotation on a plastic 



The form and size of the earth have been 
accurately determined by scientific methods. 
The polar diameter has been found to be 
7,900 miles, and the equatorial diameter 26 
miles greater. The average circumference 
has been found to be 24,860 miles, and the 
circumference at the equator 24,900 miles. 
The earth therefore is not 'a perfect sphere, 
but is flattened at the poles. In exact terms, body, 
it is an oblate spheroid. The term applied 
to a sphere that has its polar diameter greatest is prolate spheroid. 
These two modifications of the spherical form are illustrated by an 
orange and a lemon as in Fig. ii. 

The spheroidal form of the earth is supposed to have been caused 
by rotation when its was in a plastic condition. To illustrate the effect 
of rotation on a plastic body, take a strip of tin plate about two feet 
long and an inch wide; punch a hole in each end and also one in the middle. 
Bend the strip into a hoop and pass a wire through the holes and solder 
the two ends to the wire. Spin the metal hoop ^y rotating the wire 
between the fingers and note the effect indicated by the dotted lines in 
Fig. 12. 

REVIEW. I. State three proofs of the spherical shape of the earth. 2. What is the 
difference between the polar diameter and the equatorial diameter? Define oblate 
spheroid; prolate spheroid. 3. Illustrate the effect of rotation on a plastic body. 



CHAPTER III 



THE EARTH'S MOTIONS AND THEIR EFFECTS 

Rotation and Revolution. These two motions of the 
earth may be illustrated by a spinning top which is moving 
about a center. If the axis of the top always points in the 
same direction and is inclined as the earth's axis is inclined, 
it will correctly represent the position and motions of 
the earth. The motion which the top would have if it 
remained in the same position is called rotation, while its 
onward motion around a center is called revo- 
lution. If the earth had no motion of rotation 
all places on its surface would have six months 
of daylight and six months of darkness during 
the time of one revolution. Again, if the earth 
remained always in one position and did not 
revolve about the sun, there would be no 
change of seasons. In this case, owing to the 
inclination of the earth's axis, the south frigid 
zone would havfe perpetual night if the position 
of the earth were at aphelion. If its position 
were at perihelion the north frigid zone would 
have perpetual night. If the position of the 
earth were at either equinox, or if 
the axis were perpendicular to the 
plane of the earth's orbit, all places 
on its surface would have days and 

Fis*. I*?, Foucsult's cx~ 
nights of equal length throughout periment, proving the rotation 

t>ip vpflr °^ ^^^ ^^^^^ ^'^ means of a 

Liic ycdl. vibrating pendulum. 

14 




THE EARTH'S MOTIONS AND THEIR EFFECTS 15 

The time required by the earth to make one rotation is 
a day of twenty four hours. An object at the equator, 
therefore, is moving at the rate of about one thousand 
miles per hour, while the velocity of the earth in its motion 
of revolution is, as we have seen, slightly greater than this. 

An interesting proof of the rotation of the earth Is furnished by 
Foucault's experiment. He suspended a heavy pendulum from the 
dome in the cathedral of Notre Dame. Underneath it was placed a 
vessel containing sand. The pendulum was provided with a projecting 
tip at its lower end, as shown in Fig. 13. Such a long, heavy pendulum 
when set in motion will continue to vibrate for many hours in the same 
direction. As the earth rotates beneath it, the tip makes lines across 
the bed of sand, which extend through a complete circumference every 
twenty-four hours. 

Direction on the earth's surface is determined by the direction of 
the axis and by the motion of rotation. The extremities of the axis 
are the north and south points, while the direction of rotation is called 
east. The north point may be found by observing the Polar star, or by 
means of the compass. The direction opposite to east is west. In the 
northern hemisphere the south point may be located by observing the 
position of the sun at noon. 

Direction may also be determined by means of an ordinary watch. 
If the watch be held so that the hour hand points toward the sun the 
south point will be half way between this line and the twelve o'clock 
mark on the watch. 

The Revolution of the Earth around the sun takes place 
in a trifle less than 365/^ days. Its orbit, or path, is an 
ellipse, but very nearly circular. The circumference of 
the orbit is 584,600,000 miles. The velocity, or rate of 
motion, as above stated is therefore about 18 miles a second. 
As the sun is located at one of the foci, its distance from 
the earth varies from 91,500,000 miles in December to 
94,500,000 in June. 

The Change of Seasons is not due to the varying distance 
of the sun from the earth, but to the direction in which 
the sun's rays fall upon it and to the varying length of the 
day. We have observed that the sun is low in the sky in 



i6 



PHYSICAL GEOGRAPHY 




Fig. 14. The earth in its orbit, showing its position each month. 



winter and high in summer; and also that the higher it is 

the longer its daily path in the sky. We may say that the 

length of the day varies according to the height of the sun. 

In Fig. 15 the dotted curved lines represent the apparent path of 
the sun through the sky and the length of the day at the beginning of 
each season. On December 21st, winter begins and the sun is at its 
lowest position. This is the winter solstice (sun-stop). During the 
next three months it rises to the middle curve, when the days and nights 
are equal in length and the sun rises in the true east and sets in the 
true west This is the time of the vernal equinox. By June 21st, 
the summer solstice, the sun has reached the highest curve, and 
summer begins. After this date the sun returns to the autumnal 



THE EARTH'S MOTIONS AND THEIR EFFECTS 












equinox on September 2ist, and three months later, to the winter 
solstice. It will be noticed that the place of sunrise and that of sunset 
in the northern hemisphere is south of the true east and west during 
the winter, and north of these points during the summer. 

The longer the day is, the more heat the earth receives. 
At night the earth gives up its heat. When the nights are 
shorter than the days, the earth receives more heat than 
it gives up. Hence the heat accumulates. This explains 
why the month of August may be warmer than June 
although the 
days are shorter. 
But the sun's 
rays are more 
direct in June 
than in August, 
and convey 
more heat to the ^^^ 
earth, because 
they are spread 
over a smaller 
surface and also 
because less of 
their heat is 
absorbed by the 
atmosphere. 

The Explana- 
tion of the Sun's 
Apparent Motion and of the changes in the seasons and in 
the length of the day is found in the revolution of the earth 
about the sun and the inclination of its axis to the plane of 
its orbit. The amount of the inclination is 23^°. Since 
the axis always points in the same direction, it is plain 
that when the earth is at the position indicated by June 21, 




SUNRISE 



Fig. 15. The earth's daily path through the sky at dif- 
ferent seasons. Notice the place of sunrise and sunset. 



PHYSICAL GEOGRAPHY 



in Fig. 17, the north pole of its axis will be turned toward 
the sun. At this time the sun will appear north of the 
equator and long days and summer will prevail in the 
northern hemisphere. On December 21, precisely the 
opposite conditions will prevail. In March and September 
the axis will be perpendicular to a straight line connecting 
the center of the sun with the center of the earth. Hence 
both northern and southern hemispheres will be equally 
lighted up, and the days and nights will be equal all over 
the earth. 

Varying length of Day and Night. The length of the 
day in the northern hemisphere increases as the sun passes 





Fig. 16. Position of the earth at 
the time of the winter solstice. 



Fig. 17. Position of the earth at 
the summer solstice. 



from the winter solstice to the summer solstice, and de- 
creases in returning. 

Let Fig. 16 represent the position of the earth at the winter solstice, 
December 21. The rays are vertical at the tropic of Capricorn and the 
whole south frigid zone is lighted up. What is true in the northern 
hemisphere.'' What do the circles show about the length of day and 
night.'' On March 21, the time of the vernal equinox, the sun's rays 
are vertical at the equator. What shows the equality in the length 
of the days and nights at this time.? On June 21, the longest days are 



THE EARTH'S MOTIONS AND THEIR EFFECTS 



19 




found north of the equator and the shortest days are south of it. Which 
zones have summer? Which winter? The position of the axis would 
be precisely the same on September 21 as on March 21. Remembering 
this, how long would the day be at 
the north pole? At the equator? 
What can you say of the length of 
the days and nights between the 
equator and the poles at this time? 

The Earth and Man. Of all 

the planets, the earth is the 

one best fitted for human life WA ^7J ^^ 

as we know it. If it were too 
far from the sun the cold could 
not be endured; and if too 
near, the heat would be too 

p-reat The mndpratp inrli Fig. 18. The position of the earth 

great, ine moaerate men- at the time of the equinoxes. 
nation of the earth's axis allows 

an agreeable change of season and makes the larger part 
of the earth habitable. What would be the effect if the 
inclination were 50 degrees.^ What if there were no incli- 
nation of the axis? 

REVIEW. I. How does a top illustrate the rotation and revolution of the earth? 
2. State the chief effects of each of these motions. 3. What would be the result if the 
earth did not rotate on its axis? What if It did not revolve about the sun? 4. Compare 
the velocity of the earth's motion of rotation with that of Its revolution. 5. Describe 
the different methods of finding direction on the earth. 6. Why does the distance of the 
earth from the sun vary? 7. What causes the change of seasons? 8. Describe the 
position of the sun at the summer solstice; at the winter solstice; at the equinoxes. 9. At 
what circles is the sun vertical on each of these dates? 10. Why is the heating effect of 
the vertical rays of the sun greater than that of slanting rays? 11. Explain the cause of 
the sun's apparent motion in the sky. 12. What Is the effect of the inclination of the 
earth's axis? 13. What points on the earth's surface have the longest day and the 
longest night? 14. Where are the days and nights equal throughout the year? 

15. What can you say of the days and nights between the equator and the poles? 

16. Why is the earth well fitted for the home of man? 



CHAPTER IV 



TIME AND DISTANCE ON THE EARTH 

Location on a Sphere. Just as in our cities we locate 
places by means of streets and avenues, so on a sphere we 
have for this purpose meridians and parallels. Meridians 
are lines drawn on a sphere from pole to pole. Two 

meridians on opposite sides of the 
sphere make a meridian circle. 
The equator is drawn east and 
west midway between the poles. 
Circles drawn in the same direc- 
tion as the equator are called 
parallels. 

Latitude and Longitude. Dist- 
ance north of the equator is 
called north latitude; south of 

l^'ig. 19. Parallels and meridians, 1 . . 11 J -t-U 

showing the meeting of meridians at tnc CquatOr It IS CalleCl SOUtn 

the poles, and the varying length of latitude. In reckoning longitude, 

parallels. do J 

the meridian passing through 
Greenwich, London, is taken as the standard meridian. 
Distance east of it is called east longitude, and west of it, 
west longitude. The location of a place on the earth's 
surface is given by naming the parallel and meridian that 
intersect at that point. Thus New York City is in 
longitude 74°, o\ 3" West, and in latitude 40°, 4.2 , 43'' 
north. The length of a degree of latitude at the equator 
is 68.7 miles; but owing to spheroidal shape of the earth 
(see page 13), it increases to 69.4 miles at the poles. 




TIME AND DISTANCE ON THE EARTH 



21 



A degree of longitude at the equator is ^^^ of that 
circle, which is equal to 69! miles. But as the distance 
between meridians decreases as we approach the poles, the 



NORTH POLE 




iooCe. 




SOUTH POLE 



SOUTH POLE 



Fig. 20. The division of the equator in- 
to degrees of longitude. 



Fig. 21. A meridian circle divided into 
sections of twenty degrees latitude each. 



length of a degree of longitude depends upon the latitude 
where it is measured. • In the latitude of New York City 
it is 53 miles. At London, latitude Si>^° N., it is about 
45 miles. At 80° it is 12 miles, while at the poles, where all 
meridians meet, it is nothing. 





Length 


OF 


One 


Degree 


IN 


Statute Miles 


In Latitu 


de 0°, 


1° 


Latitude 


= 68.70 miles, 


1° Longitude = 69. 1 7 miles. 




10°, 






i 


= 68.72 




= 68.12 " 




20°, 








= 68.78 




" =65.02 " 




30°, 








= 68.87 




= 59-95 " 




40°, 








= 68.99 




" • =53-06 " 




50°, 








= 69.11 




= 44-55 " 




60°, 








= 69.23 




= 34-67 " 




70°, 








= 69.32 




= 23.72 " 




80°, 








= 69.38 




" =12.05 " 




90°, 








= 69.40 




"■ =00.00 " 



How latitude and longitude are found. Latitude may 
be found by observing the height of the Polar star, or of 



22 



PHYSICAL GEOGRAPHY 



the sun, above the horizon. At the equator the Polar star 

appears on the horizon, and rises as the observer moves 

north. At the pole it is directly over head. Hence, the 

height of the star above 

the horizon will be 

equal to the latitude 

of the observer. 

The usual method of find- 
ing latitude at sea is by 
taking an observation of 
the sun at noon. By means 
of the sextant its apparent 
altitude above the horizon 
is determined in degrees, 
minutes, and seconds. To 
this observed altitude, cor- 
rections are made for re- 
fraction of the sun's rays, 
for the "dip" or depression 
of the horizon owing to the 
position of the observer, for 
parallax, for variation from 
Greenwich time, and for in- 
accuracies in the instru- 
ment. The semi-diameter 
of the sun is also subtracted 
from the observed altitude. 
This corrected altitude is 
then subtracted from 90° 
and the remainder is the 
sun's "zenith distance." 
The sun's distance north 
or south of the equator is 
known as declination, and 
is given in the nautical 
almanac for every day of the year at 12 o'clock noon, Greenwich time. 
If the observer is on the same side of the equator as the sun, he adds 
the declination of the sun to its zenith distance. This sum is the 
latitude of the observer. But if the observer is on the side of the 
equator opposite to the sun, his latitude will be the difference between 
the zenith distance and the declination. The "sextant" is an elabo- 
rate instrument requiring much practice to use it correctly. 




Fig. 22. Taking the altitude of the sun by 
means of a sextant. 



TIME AND DISTANCE ON THE EARTH 



23 



Longitude at sea is found from its relation to time. Since 
a point on the earth rotates through 360° of longitude in 
24 hours, it will pass through 15° in one hour, or 15' in one 
minute. That is, time in hours, minutes, and seconds 
is tV of the equivalent longitude. Now suppose a ship 
wished to know its longitude at sea. It has on board a 
very accurate clock keeping Greenwich time. By observ- 
ing when the sun crosses the meridian, the ship obtains 




standard time 
/ belts';^ 

lio LA_b. 



IQS 



Fig. 23. Standard time belts. 

its own local time. Suppose the Greenwich time is 9 
o'clock and the ship's time 12 o'clock. This is a difference 
of three hours. Since one hour equals 15°, three hours 
equals 45°, and the ship will be in 45° east longitude. If 
the ship's time had been three hours earlier than the 
Greenwich time, it would be 45° west in longitude. Why.? 
Local and Standard Time. Time obtained from the sun 
at any place is called solar, or local, time. Since all places 



24 



PHYSICAL GEOGRAPHY 



in different longitudes must have different local time, the 
railroads of the United States and other countries have 
agreed upon systems of standard, or railroad, time. By this 
system it is arranged that the time shall change one hour 
for every 15° of longitude. By this method our country is 
divided into four time belts, so that one in traveling from 
the Atlantic coast to the Pacific coast will need to change 
a watch only four times. When traveling westward, a 
watch must be set back one hour on crossing each meridian; 
but when traveling eatward it is set ahead. On the merid- 
ians, solar and standard time will be the same. Half-way 
between them, there will be a difference of 73^° or 30 
minutes of time. 

As a matter of practice, railroads do not change their time exactly 
at the meridian, but at important centers that are nearest the meridian, 
as Buffalo, Pittsburgh, etc. (see map of the Time Belts). 

International Date Line. The day begins at midnight 
and lasts until the next midnight. Since it is desirable 

that all nations 
should have the 
same number or 
date for each day, 
it has been agreed 
that the new day 
shall begin on the 
iSothmeridian. At 
midnight, there- 
fore, the new day 
begins and follows 
T.. Tn • 1 , ■ r , • 1 J the sun westward 

rig. 24. illustrating the relation oi longitude and 

time. The meridians are drawn at intervals of thirty arOUud the WOrld. 

degrees. The time on each meridian is shown at the hour xtx. . ■■ 

of noon on the prime meridian. Wlien it reacJieS 




TIME AND DISTANCE ON THE EARTH 25 

this "International Date Line," as it is called, a new day 
has begun. Thus when it is Sunday on the east of the 
line, it will be Monday on the west of it. If a ship should 
cross the line sailing east, it would have two Sundays; 
but when sailing west a day is dropped. 

REVIEW. I. How are places located on a sphere? 2. Define meridian, parallel, 
meridian circle. 3. Name the other leading circles drawn on the earth. 4. Great and 
small circles. 5. Define latitude, longitude, north and south latitude, east and west 
longitude. 6. Why do degrees of longitude vary in length? 7. Describe the method 
of finding the latitude of a place. 8. How does a sailor determine his longitude? 9. 
What is meant by local time? By standard time? 10. Describe the use of time belts. 

11. What change does a traveler make in his time when going east? When going west? 

12. International Date Line. 



CHAPTER V 




THE EARTH'S MAGNETISM 

The Mariner's Compass. If a magnetized needle be 
suspended anywhere so that it may turn freely, it will 
point to two places on the earth's surface, which are called 
the north and the south magnetic poles. When such a 
needle is fastened to a card on which the points of the 

compass are written and mounted 
so that it may turn freely, we have 
an instrument that enables the 
sailor to find his way when the 
land and the stars cannot be seen. 
If a needle horizontally sus- 
pended be moved along a bar 
magnet, one end of it will be 
drawn toward the north pole of 
the magnet, and the other end tow- 
ard the south pole. This prop- 
erty of attracting iron and steel, 
whether exhibited by a magnet or 
by the earth, is called magnetism. 
The earth behaves exactly like 
the bar magnet, and hence has 
the property of magnetism. 

The magnetic poles of the earth 

are not the true north and south 

poles. The north magnetic pole 

is in the northern part of North 

26 




Fig. 25. A magnetic needle 
mounted horizontally. 2. A dip- 
ping needle. 



THE EARTH'S MAGNETISM 



27 




Fig. 26. A compass card. Naming all 
the points on the card is called "boxing the 
compass." 



America, near latitude 70° 
north and longitude 97° 
west. The south magnetic 
pole is near latitude 73° 
south and longitude 155° 
east. 

Dipping Needle. The 
location of the magnetic 
poles is found by means of 
a dipping needle. When 
the needle points directly 
downward, the pole has 
been found. Since the mag- 
netic poles are not coinci- 
dent with the true north and south, the compass will 
vary from these directions. The amount of such magnetic 

variation is called declina- 
tion. 

Declination. On the compass 
shown in Fig. 27 the declination is 
about 5°. The line along which 
the needle points is the magnetic 
meridian. When a magnetic merid- 
ian passes through the north and 
south geographical poles as well as 
the magnetic poles, it is called a 
"line of no variation." Along 
such lines the needle points to the 
true north and south. The sailor 
is provided with a chart which 
shows the exact amount of declina- 
tion all over the earth. 

The reason for the magnetism 
of the earth is not certainly known. 
It is thought that it may be caused 
by currents of electricity produced 
by the sun's rays as they pass 




Fig. 27. A compass showing the decli- 
nation of the needle. 



28 



PHYSICAL GEOGRAPHY 




Fig. 28. Lines of magnetic declination in the United States. 






Fig. 29. The cut on the right shows how a bar of soft iron is made magnetic by 
passing an electric current around it. The cut on the left shows how an electric current 
may be caused by heating two pieces of metal joined together. These metals, owing to 
their nature, take up heat unequally, and hence the current is generated. 



THE EARTH'S MAGNETISM 29 

around the earth from the east to west. If a piece of soft iron be 
wound with a coil of wire, and an electric current sent through the wire, 
the iron will become magnetic; again, if two metals be soldered together 
and the point of the union be heated, a current of electricity will 
be established in the wires. These two experiments show how heat may 
produce electricity and how electricity may produce magnetism. 

REVIEW. I. Describe the construction of the mariner's compass. 2. To what 
places on the earth does the needle point? 3. What is the effect of moving a suspended 
needle along a bar magnet? 4. Define magnetism. 5. State the location of the magnetic 
poles of the earth. 6. In what places does the needle point to the true north and south? 
7. What allowance must the mariner make at other places on the earth? 8. Explain the 
use of the dipping needle. 9. What is said about the cause of the earth's magnetism? 
10. What experiments tend to prove this? 



CHAPTER VI 



PHASES OF THE MOON — ECLIPSES 

Phases of the Moon. The sun and the stars are luminous 
(light-giving) bodies; but the planets and moons are opaque, 
and shine only because they reflect the light which they 
receive from luminous bodies. 

Close all the windows of the school room but one, and place a 
globe having a polished surface where the light may strike upon it. 
If you walk around the globe, you may distinguish upon it phases of 
light similar to those of the moon. 

Since the moon revolves about the earth, it will sometimes 
be on the same side of the earth as the sun. It may also be 
on the side of the earth opposite to the sun or may make 

any angle with 
the sun and 
earth. The 
amount of light 
that the moon 
reflects to us de- 
pends upon its 
position with 
reference to the 
sun and earth. 
The changes in 
the moon's ap- 
pearance are 
called phases 
(Fig. 31). The 
earth's orbit and 




Fig. 30. Light reflected from a polished globe showing 
crescent. The observer is supposed to be in front of the pic- 
ture at an angle with the lamp and the globe. 



30 



PHASES OF THE MOON — ECLIPSES 31 

the moon's orbit are not in the same plane; hence the 
moon may be on the same side of the earth as the sun and 




Fig. 31. The phases of the moon. The light comes from above the cut. 

not be on the straight Hne connecting them. If in Fig. 32 
you imagine the figure of the sun cut out and lifted perpen- 
dicularly about an inch above the page, you may see that 
the sun, moon, and earth will not be in the same straight 



32 



PHYSICAL GEOGRAPHY 



line. It will also be apparent that the moon will be un- 
equally lighted up in its revolution about the earth. 

Eclipse of the Moon. The earth, being an opaque body, 
casts a long conical shadow into space. As this shadow 
extends outward into space far beyond the path of the 
moon, it often happens that the moon passes through the 
shadow in its monthly journey around the earth. It is 
then dark, or "eclipsed." An eclipse occurs at or near 
the time of full moon. Only a part of the moon may be 
in the shadow. It is then a "partial" eclipse. If the 
entire surface is in the shadow, it is a "total" eclipse. 
The partially shaded region in the diagram darkens the 
moon slightly when it passes through, but it is not eclipsed 
until it enters the umbra, or region of total shadow. 

An eclipse of the sun may occur when the moon comes 
between the sun and the earth. If you hold an object 
between your eye and the sun, the shadow of the object 
falls upon the eye and cuts oif part of the light. If the 
object be moved closer to the eye, its shadow is larger and 
cuts off more light; if it be moved away from the eye, the 
shadow is smaller and cuts off less light. If it be moved 
far enough away, the shadow will not reach the eye and 
hence no light is cut off. The distance of the moon from 
the earth varies from about 222,000 to 253,000 miles. 




MOON 

Fig. 32. The relative positions of the moon, earth, and sun, at time of total eclipse of 
the moon. 



I 



PHASES OF THE MOON — ECLIPSES 



33 



The length of the moon's shadow averages 232,000 miles. 

It is clear that the shadow will sometimes reach the earth, 

but oftener will fail to do so. When it does reach the 

earth, the people who livein the region where the shadow 

falls will see an eclipse of the sun. 

The moon may entirely cover the sun and cause a total eclipse or 
it may pass as a black crescent across the sun's edge and thus cause a 




EARTH 



SUN 



Fig. 33. Relative positions of the sun, moon, and earth during an eclipse of the sun. 



partial eclipse; or It may pass across the center of the sun's disk at 
such a distance from the earth that a ring of light will be seen around 
the outer edge of the sun. This is called an "annular," or ringed 
eclipse. 

REVIEW. I. Luminous and opaque bodies. Illustrations of each class. Describe 
the motion of the moon. In which position does it send us the most light.'' When is it 
a "dark" moon? What is meant by new moon and full moon (page 31)? 2. What is 
the cause of an eclipse of the moon.^ Why can an eclipse occur only at or near the time 
of full moon? Total eclipse. Partial eclipse. What causes an eclipse of the sun? Why 
is the moon nearer the earth at certain periods than at other periods? Explain how a 
total eclipse is caused; a partial eclipse; an annular eclipse. 



CHAPTER VII 



ATMOSPHEDE 




':/ 



GENERAL FEATURES OF THE EARTH 

The Four Spheres. We may describe the earth as 
composed of four spheres having a common center. The 
inmost of these, called the centrosphere, is a great ball 
forming the interior of the earth, while the others are 
hollow spheres enclosing it like the coatings of an onion. 
The centrosphere is over a hundred times as great in bulk 

as all the other parts of the 

earth together. It seems to 
consist of hard rock which 
is intensely hot, and which 
is kept from melting only by 
the great pressure exerted 
upon it by the crust of the 
earth. 

The Lithosphere. Enclos- 
ing the central sphere is a 
Qp E^Al^H crust composed of many va- 
rieties of rock and having a 
thickness varying from ten 
to twenty miles. This is 
usually called the earth's crust. The lithosphere is mainly 
composed of rock arranged in layers, or stratified rock. 
We may observe such rock where cuts have been made 
through hills for railroads. The walls of canyons carved 
out by rivers also show layers of rock of various colors. 
The common kinds of stratified rock are sandstone, shale, 



HYD150- 
SPHEliE. 



CEhTDOSPHEliE. 
SECTION 

Fig. 34. A section of the earth, 
showing its structure. 



34 



GENERAL FEATURES OF THE EARTH 



35 



conglomerate, and limestone. Sandstone is made of grains 
of sand held together by some kind of cementing material. 
Shale consists of mud which has dried and hardened under 
pressure. Slate and bluestone are varieties of shale. 
These rocks are easily split into sheets of varying thick- 




Fig. 35. Gorge of the Genesee river showing layer rock. 

ness and are useful for sidewalks and for covering roofs. 
Conglomerate consists of gravel or coarse pebbles bound 
together in the same way as sandstone. Coarse con- 
glomerate is sometimes called pudding-stone. Limestone 
is made of the shells of animals that once lived in sea water. 
These have been ground up by the actions of the waves 
and breakers along the shore and mixed with mud and 
sand. Afterwards they have been buried deep under the 
deposit brought down by streams, and by heat and pressure 
have been changed into firm rock. 

History of Layer Rock. Nearly all the layer rock in 



36 



PHYSICAL GEOGRAPHY 



the world has been made of fragments of older rock which 
have been worn away from the land surface and carried 
down to the ocean by rivers. This material, in the form 
of mud or sand, has been spread out over the ocean bottom 
and afterwards hardened into rock. No matter where 
stratified rocks occur, whether in lowlands or on the highest 

mountains, they 
were at first 
laid down under 
water. It seems 
strange that 
rocks now a part 
of mountains 
thousands of 
feet in height 
were once at the 
bottom of some 
ocean. Yet we 
know this is true 
because the 
rocks contain the remains of plants and animals which can 
only live in salt water. By means of these remains, or 
fossils, we are able to learn much about the formation of 
rocks and about the succession of plants and animals that 
have existed upon the earth. It is evident that great 
changes must have taken place upon the earth in order to 
lift the bottom of the ocean up into hills and mountains. 

Stratified rock is seldom found in the form or position in which it 
was at first laid down. Much of it has been changed, not only in level, 
in appearance, and in texture, but it has been folded, twisted, crumpled, 
and carved by the forces of nature. Much of it after having been 
lifted up into hills and mountains has again been worn away by the 
action of the elements and carried back to the ocean or spread out 
along the lower courses of rivers to form alluvial plains and deltas. 




Fig. 36. A fossil fish taken from rocks near Boonton, 
New Jersey. 



GENERAL FEATURES OF THE EARTH 



37 



Much of it has decayed to form the soil which composes the outer 
layer of the earth's crust and which supports innumerable forms of 
vegetation and the animals that depend on plants for food. 

Crystalline rocks. Rock that has cooled after melting, 
or layer rock which has been changed by the action of heat 
so that little or 
no trace of the 
original forma- 
tion remains, is 
called crystal- 
line or metamor- 
phic (changed) 
rock. Such rock 
is composed of 
crystals of va- 
rious forms 
packed solidly 
together. Gran- 
ite, marble, 
and gneiss are 
the common 
varieties of 
crystalline rock. 
Granite is crys- 
tallized sand- 
stone or conglomerate. Marble is crystallized limestone. 
Gneiss and various forms of rock containing mica bear 
traces of the original layer formation. Rocks which have 
cooled after fusion are called igneous rocks. Lava and 
basalt are the usual varieties (Fig. 40). In the neighbor- 
hood of boiling springs and geysers, crystalline rocks are 
found which have resulted from the cooling of the hot 
water containing rock material in solution. All varieties 




Fig. 37. View in a marble quarry, near Rutland, Vermont. 
Notice the regular structure of the layers. 



38 



PHYSICAL GEOGRAPHY 



of precious stones have crystallized from solution or have 
been formed through the action of intense heat. 

Metamorphic rock is found everywhere underlying the layer rock 
and extends an unknown distance toward the center of the earth. 
Much of it, especially volcanic rock, is found at the surface spread out 
in layers or in ridges and mountains that have forced their way upward 
through pressure within the crust of the earth. Crystalline rocks are 
usually very hard and are well adapted for building purposes. 

Soil. All rock, whether stratified or crystalline, when 
lifted to the surface and exposed to the action of the 

elements begins 
to decay (Fig. 
38). The rapid- 
ity of decay de- 
pends upon the 
hardness of the 
rock exposed. 
Shales and sand- 
stones decay 
most easily, but 
the harder crys- 
talline rocks 
decay very 
slowly. After a 
time, therefore, 
the surface of 
the rock is over- 
layed by a layer of loose material which we call mantle rock 
or soil. The soil is of the greatest value to mankind, since 
it supports all the plant life of the earth, without which no 
animal life could exist. Soil is found everywhere on the 
land surface except on the steep sides and summits of hills 
and mountains. It varies in thickness from a few inches 




Fig. 38. Sectional view showing soil and rpcic layers. 
At the bottom of the cut is shown hard, crystalline rock. 
Overlying this is stratified rock. Next rock is shown in va- 
rious stages of decay. Above the decayed rock is a layer of 
soil with vegetation growing above it. 



GENERAL FEATURES OF THE EARTH 39 

in elevated regions to scores of feet in lowland plains. The 
common varieties of soil are sand, clay, and gravel and 
mixtures of these. Sand and clay together form loam. 
When loam contains decayed vegetable or animal matter 
it becomes fertile and suitable for the cultivation of plants. 
Decayed limestone or phosphate rock adds greatly to the 
fertility of the soil. Soil must be loose enough to allow 
air and moisture to enter it, and it requires a mixture of 
clay or an underlying stratum of waterproof rock, so that 
it may retain moisture for a considerable time. Marl and 
peat are varieties of soil used as fertilizers. Marl is a 
mixture of clay and lime formed under water from the 
remains of shellfish and the sediment of rivers. Peat is a 
black soil found in swamps, and is derived from decayed 
vegetable matter. When dried it is useful as fuel. The 
character of soil in general depends upon the kind of rock 
from which it was formed. Limestone and lava when 
decayed form the best bases of a fertile soil. The value 
of soil depends upon the proportion of plant food which it 
contains. Since all plants do not require the same kind 
of food it becomes an important part of scientific agriculture 
to raise plants on the soil best suited to them or to sup- 
ply to the soil the food elements necessary to produce the 
crops desired. 

Minerals. All soils and the rocks from which they come 
are composed of minerals. The word mineral is a term 
which applies to all substances that are not derived from 
plant or animal life. The atmosphere, the waters, and 
the great bulk of the earth belong to the mineral, or inor- 
ganic kingdom. The common varieties of minerals are 
quartz, feldspar, mica, lime, and carbon. These exist in 
many forms and combinations. The various metals and 



40 



PHYSICAL GEOGRAPHY 



ores are also among the common minerals. Sand is com- 
posed of minute grains of quartz, mica, and other minerals. 
Feldspar when decayed forms clay. Carbon comes from 
decayed plants, and lime from the shells and bones of 




Fig. 39. A marl bed in New Jersey. 

animals. Minerals when transparent, become gems. The 
diamond is pure crystallized carbon. The amethyst, opal, 
agate, onyx, and other gems consist of crystalline forms of 
silica or quartz. 

Hydrosphere. The meeting place of the gaseous part 
of the earth with the solid and liquid parts is called its 
surface. We learn from the study of the surface of the earth 
that at some time in its history it consisted entirely of the 
waters of the ocean. But at the present time the ocean 
composes only three fourths of the surface, while the remain- 
ing fourth consists of the continents and islands. The 



GENERAL FEATURES OF THE EARTH 



41 



ocean surrounds the continents on every side and receives 
all the streams that flow from them. It is thus broken 
into several large divisions and many smaller ones which 
have received appropriate names. During past ages the 
ocean floors have sunk, while the continents have risen. 




Fig. 40. Columns of volcanic rock near Orange, New Jersey. 

The effect of this has been to quicken the action of streams 
and to increase the amount of sediment which they carry 
to the ocean. As a result of this the surface of the land 
has become very irregular while the ocean floors have been 
leveled by the deposit of sediment and by the accumula- 
tion of plant and animal remains which have sunk to the 
bottom. 

The Continents. The parts of the earth which gradually 
rose above the waters have grown into the great masses 
of land which we call continents. Two of these masses 
begin at the north pole and extend southward. The larger 



42 



PHYSICAL GEOGRAPHY 



includes the grand divisions of Asia, Europe, and Africa, 
and the smaller, those of North America and South America. 
The third great land mass lies wholly southward of the 
equator, forming the continent of Australia. Another great 
land mass, which has been only partially explored, lies in 
the south frigid zone. It has received the name Antarctica. 
Partially enclosed by the great land masses are the four 
leading divisions of the ocean, the Atlantic, Pacific, Indian 
and Arctic. 

Four of the continents are built on the basin model; that is, they are 
high near the borders and low in the interior. Asia and Africa, however, 
have high interior regions and low bordering plains of varying breadth. 
The highest mountains are found along the margins of the largest and 
deepest oceans, while the lowest mountains, which are also the oldest, 
border the smaller and shallower ocean, the Atlantic. 

The Atmosphere. The solid and liquid parts of the earth 
are surrounded by the lighter, gaseous atmosphere, which 
extends for many miles outward from the surface. Though 
the atmosphere is the lightest part of the earth's substance, 
it presses down upon the surface with considerable force 
and fills all the cavities in the rocks and soil. It finds its 
way down to the roots of plants and helps their growth. The 




Fig. 41 

Fig. 41. Cross sections of North America and South America, showing basin-like 
structure. Notice that the highest mountains are on the western border, and that the 
low mountains border the Atlantic ocean on the east. 



GENERAL FEATURES OF THE EARTH 43 

oxygen of the air is necessary to all animal life. It is taken 

up by the waters, and even the deepest parts of rivers, 

lakes, and the oceans contain enough of it to keep alive the 

fish and other creatures that live there. 

The origin of the continents may be explained by referring to the 
nebular theory. This theory tells us , that after the earth's crust was 
formed, the interior continued to cool and contract until it became 
smaller than the crust. The latter was therefore drawn toward the 
center of the earth by its own weight, and being too large to fit the 
shrinking interior, it rose up here and there in broad folds like a gar- 
ment that is too large for the body, or a carpet which is too large for 
a floor. 

REVIEW. I. Describe the four spheres that compose the earth. Which is the 
greater? 2. What is meant by stratified rock? 3. Name the common varieties and 
tell of what each is composed. 4. Explain how stratified rock has been formed. 5. What 
do we learn from fossils? 6. What is crystalline rock? 7. Name three varieties. 8. 
Where is crystalline rock found? 9. For what is it useful? 10. What is the origin of 
soil? II. Describe the common varieties. 12. What is said of its thickness? 13. Name 
the leading minerals. 14 What is meant by the mineral world? 15. What are gems? 
16. Describe the ocean. 17. Why is it supposed that it once covered the entire earth? 
18. How does the surface of the land compare with the ocean floors? 19. How is the 
origin of the continents explained? 20. Describe the atmosphere. 21. Why is it farther 
from the center of the earth than the other "spheres?" 



CHAPTER VIII 



MOUNTAINS AND PLATEAUS 

Occurrence and Formation. Any elevation of land 
above a moderate height is called a mountain. The moun- 
tains of the world are usually found in long rows, or ranges. 
A number of ranges when grouped together form a moun- 
tain chain or system. Mountain ranges and systems vary 
greatly in breadth and elevation. They consist usually of 
a vast mass which has been raised above the general level 
of the country, from the summit of which rise peaks more 
or less rugged, according to the resisting nature of their 

materials and to 
the length of 
time that they 
have been acted 
upon by the 
elements. 

On plains the 

rock layers are 

usually found in 

a horizontal 

position, but 

in mountain 

ranges they are 

bent, folded, 

crumpled, and broken as though they had been raised 

violently upward or forced together by enormous lateral 

pressure. If a number of sheets of loose paper be pressed 

44 




Fig. 42. Faulted strata. The center of the cut shows a 
fracture on the right of which the rock layers have sunk so 
that the strata on one side of the fracture do not coincide with 
those on the other side. 



MOUNTAINS AND PLATEAUS 



45 



together from the ends, the folds which result may be 
compared with the folds of strata found among moun- 
tains. Sometimes the strata are broken, and the rocks on 
one side of the fracture are lifted far above the correspond- 
ing rocks on the other side, producing a fault. 

The forces which have produced the phenomena just 
described have been alluded to on page 44. The chief 
cause, however, of the rugged nature of mountain regions, 
as we see them to-day, is found in the agencies of erosion 




Fig. 43. Block structure of mountains. 



and in the fact that the rocks vary greatly in hardness. 
As the softer parts are worn away by the elements, the 
harder rocks are left in jagged peaks and serrated ridges. 
Swift streams have carved out deep valleys and canyons, 
leaving the sloping sides in the form of projecting cliff 
terraces and sometimes in perpendicular rocky walls. 

Mountain Structure. In some regions, notably in north- 
ern California and in southern Oregon, the ranges overlie 
one another like a series of blocks, which have been tilted 
so that the summit of one block overlies the base of the next 
one. Such a structure is known as block structure. 
Among such mountains the streams follow the troughs thus 
formed wearing out valleys with a long slope on one 
side and a short and abrupt slope on the other. Other 
mountains have a folded structure like that shown in 
Fig. 48-a, In this case the fold seems to have resulted 



46 



PHYSICAL GEOGRAPHY 



from lateral pressure. In other cases a broad, low, moun- 
tain fold or a plateau has been cut into a multitude of 
separate ridges by the action of streams. Such mountains 
are known as "dissected" ranges, and occur in all 

the continents. The 
loftiest mountain peaks 
in the world, found 
among the Alps, the 
Himalayas, the Andes, 
and the Rocky moun- 
tains, consist mainly of 
long layers having an 
upward slant and 
formed of tough, re- 
sisting materials. The 
bare and lofty sum- 
mits of the Alps with 
their needle pointed 
minarets, are of the 
hardest granite, all 
the softer materials 
having been worn 
away. 

In other cases mountain ranges are composed of materials 
so uniform in texture that the entire surface has been worn 
down, forming a low plateau like that occurring in New 
England and in other parts of the Appalachian system. 
Such a low, rolling, eroded surface has received the name, 
peneplain (almost a plain). 

Rock Sculpture The western part of the United States 
affords a striking variety of sculptured rock forms. One 
of the most remarkable of these regions is the "Bad Lands" 




Fig. 44. Cliffs and pinnacles of red sandstone 
left by erosion in northeastern Arizona. 



MOUNTAINS AND PLATEAUS 



47 



of South Dakota. These consisted originally of a succes- 
sion of clay beds and sandstone. Through the action of 
streams this region has 
been dissected into 
ridges, pinnacles, and 
towers of a remarkably 
picturesque character. 
The Colorado plateau 
also affords many ex- 
amples of rocky 
remnants in the form 
of battlements and 
towers which appear 
in the distance like 
remains of gigantic 
architecture. In some 
cases where hard vol- 
canic rock has filled 
crevices and ancient 
craters, the softer 
surrounding rocks have been worn away and the lava 
left in flat topped masses called plugs, or in long ridges 
known as dikes. 

Plateaus. The long, sloping foothills of mountain ranges 
and the elevated plains found among them are known as 
plateaus. In general, any plain above 2,000 feet in height 
is classed under this head. Plateaus are generally composed 
of a variety of rock layers in a nearly horizontal position. 
The most extensive plateau system of the world is found 
among the mountains of central Asia. These are also 
the highest plateaus. The United States also contains 
many plateaus of varying elevation. The lower plateaus 




Fig. 45. Eroded rocks, Grand Canyon of the 
Colorado river. 



48 



PHYSICAL GEOGRAPHY 




Fig. 46. A butte in North 
Bismarck, along the Missouri river. 



Dakota, northeast of 



are generally good farming and grazing regions, as in the 
case of the Piedmont, the Allegheny plateau, and the 

Great Plains. 
The loftier plat- 
eaus are fre- 
quently deeply 
dissected by 
streams. Where 
this process has 
gone on long 
enough the 
canyons have 
widened into valleys bounded by low mountains and are 
adapted to the uses of man. The Colorado plateau on the 
other hand, while it has been deeply cut by that river and 
its branches, is a desolated region and offers no advantages 
to the farmer. In some cases plateaus have been almost 
entirely worn away and only a few flat topped table 
mountains with vertical sides remain. To these the names 
mesas and buttes are applied. 

Effect of Mountains on Climate. The chief character- 
istics of mountain climate are coolness and dryness. As 
temperature falls about 1° for every three hundred feet of 
ascent, the loftiest mountains are regions of perpetual 
snow, and the cold air descending from their summits has 
the effect of lowering the temperature of the entire sur- 
rounding country. The best known effect of mountains 
on climate is the fact that they are condensers of moisture 
and that the regions on the windward side of them are 
remarkable for heavy rainfall while on the opposite side 
deserts are usually found, especially in the regions of 
constant winds. On account of the dry atmosphere and 



MOUNTAINS AND PLATEAUS 



49 



its lightness, mountain regions are healthful places of 
residence for sufferers from lung diseases. The vegetation 
of mountain regions presents a continuous succession of 
species from the base to the summit. Mountains are not 
only a barrier to 
wind and rain, but 
they have also ex- 
erted a great in- 
f luence on the 
history of the world 
by preventing inter- 
communi cation. 
Remarkable exam- 
ples of this are the 
Pyrenees, between 
France and Spain, 
and the Himalayas, 
which separate 
India and China. 
It has taken cen- 
turies for the in- 
genuity of man to 
overcome the 
opposition of moun- 
tain barriers. The 
inhabitants of 
mountain regions 
are proverbial for 
their free and independent spirit, and intrenched in their 
inaccessible homes they have generally succeeded in de- 
fending themselves against enemies. 

Mountain Passes. In some cases mountains are crossed 




Fig. 47. The Khaibar pass in the Himalaya moun- 
tains. This pass forms the only highway between central 
Asia and India. It is 33 miles in length and in places 
only 40 feet in width. All the conquerers of India 
except Alexander the Great and the British entered the 
country by way of this pass. 



50 PHYSICAL GEOGRAPHY 

by valleys which run at an angle with the ranges. These 
are called transverse valleys or passes. Two such remark- 
able valleys cross the Himalayas, and they have formed the 
highway through which invaders have descended from the 




Fig. 48. A landslide in Colorado, which formed a lake by damming a stream. 

north of Asia into India. The Alps also have numerous 
passes through which in both ancient and modern times 
armies have made their way into Italy. 

Avalanches and Landslides. Owing to the heavy snow- 
fall among mountains, their slopes and summits accumulate 
vast masses which when slightly loosened by melting slip 
oif and fall with tremendous force into the valleys below, 
Am.ong the Alps such avalanches are common, and fre- 
quently entire villages are overwhelmed by them. It 
often happens also that masses of earth and rocks become 



MOUNTAINS AND PLATEAUS 



loosened among the mountains and rush down the slopes 
for miles, destroying both men and animals and sweeping 
away entire forests. Landslides sometimes fill up valleys 
and damming the streams cause lakes to form. Sometimes 
they change the course of streams by filling up their usual 
channels. Owing to the disturbance of the strata in moun- 
tain ranges earthquakes frequently occur. The dropping 
of the rocks on one side of a fracture or the sudden lifting 
of a stratum may cause an earthquake shock which may be 
felt at a great distance from the seat of disturbance. 

REVIEW. I. Describe the arrangement of mountains. 2. What is said of the rock 
layers in mountain regions? 3. How is the formation of mountains explained? 4. What 
is meant by a block structure? By dissected ranges? 5. How do you account for the 
rugged nature of mountains? 6. What is said of sculptured forms? 7. What are 
plateaus? 8. Name some of the great plateaus of the world. 9. Name the chief effects 
of mountains on climate. 10. What effect have they had upon the history of nations? 
II. What are mountain passes? 12. Describe an avalanche. A landslide. 




CHAPTER IX 



EARTHQUAKES AND VOLCANOES 

Internal Heat of the Earth. There is abundant evidence 
that certain sections of the interior of the earth, are 
intensely heated. Boiling springs, the lava and steam from 
volcanoes, and the high temperature of deep mines are 
among the many proofs. The increase of temperature as 
one descends into the earth is about i° for every sixty feet 

of descent. At 
this rate the 
heat would be 
great enough at 
the depth of 
fifty miles to 
melt all known 
rock. The 
enormous p res- 




Fig. 49. Section of a volcano. The dark lines indicate the 
course of fractures through which the naelted rock finds its 
way to the surface. 



sure of the crust of the earth would, however, keep the 
heated interior rock solid, as the melting point of solids 
depends on the amount of pressure upon them. But 
should the pressure be removed, the heated rock would im- 
mediately liquefy and flow outward as a volcano. 

Volcanoes and Lava Flows are found among mountain 
regions in every part of the earth. The volcanoes are for 
the most part burned out, but many active ones still occur 
on the borders of the Pacific ocean and in the south of 
Europe. Sometimes volcanoes burst forth at the bottom 
of the ocean. The lava, rock, and cinders that are thrown 

52 



EARTHQUAKES AND VOLCANOES 



53 



up gradually build up a volcanic cone, which may develop 
into an extensive island. Stromboli, near the northern 
coast of Sicily, is a volcanic cone which rests on the sea 
bottom, 3,000 feet below the surface, and is three or four 
miles in diameter. From a circular opening in its side, 
clouds of steam issue and occasionally the white-hot lava 




Fig. 50. Eruption at Mt. Vesuvius. 

bursts out and flows down the mountain side. The explo- 
sions and eruptions are due to the formation of steam in 
the melted rock within the crater. 

The largest volcanic island in the world is Hawaii. It 
is ninety miles long and seventy miles broad and contains 
two active volcanoes. One of these, Mauna Loa, 15,000 
feet high, has a broad, flat top containing a lava lake forty 
acres in area. From its surface jets of lava are thrown to 



54 



PHYSICAL GEOGRAPHY 



the height of several hundred feet. At times the lava 
stream breaks through fissures in the side of the moun- 
tain and streams of the liquid rock several miles wide run 
down into the sea at a distance of thirty to forty miles. 

One of the earliest and most destructive volcanic eruptions recorded 
Is that of Vesuvius, A. D. 79, which buried the cities of Pompeii and 
Herculaneum. After being lost for centuries, these cities have been 
excavated and found to be in a good state of preservation. 

A remarkable volcanic explosion occurred in 1883, on the small island 



L>:. ,-. Ik: 4^"i^' 




Fig. 51. Results of the San Francisco earthquake. 

of Krakatoa in Sunda strait. The northern half of the island was 
entirely swept away by an explosion which was heard for several 
hundred miles. Enormous quantities of rock and pumice were hurled 
out, and the sea for several miles around was so thickly covered with 
floating pumice that the course of vessels was obstructed. The dust 
blown upward was caught by air-currents and carried entirely around 
the earth. 

The most destructive volcanic eruption of modern 
times occurred on the island of Martinique in 1902. The 
city of St. Pierre was entirely destroyed and 30,000 people 
killed. The volcano of Mont Pelee stands near the city. 
For fifty years it had been inactive, and the people felt 



EARTHQUAKES AND VOLCANOES 55 

secure. But on the 8th of May, a terrific stream of hot 
water and lava burst through a break in the crater wall, 
and, following a valley down to the city destroyed every- 
thing in its path. We can compare with this disaster only 
the eruption of Mount Vesuvius, 79 A. D., which buried 
the cities of Pompeii and Herculaneum. 

The Cause of volcanic eruption is the formation of steam 
in the liquid rock that fills the craters. Water from 
underground channels flows into the hot lava and is suddenly 
turned to steam. This would cause the awful explosions 
that occur, and would make the liquid lava boil up and 
overflow. But the great lakes of boiling lava, miles in 
extent and of unknown depth, where do they come from? 
The interior of the earth is kept solid only by the great 
pressure of the rocks above it. Now, if these outer rocks 
become broken or weakened in any way by movements 
within the earth's crust, the hot rock below at once be- 
comes liquid and boils up until it finds an outlet. 

Earthquakes. In the process of mountain formation, 

as the rock layers are forced upward by lateral pressure, 

they are frequently fractured and the shock becomes an 

earthquake, which may be transmitted for thousands of 

miles. 

Bend a brittle stick across your knee until it breaks, and notice the 
shock. The rumbling of an approaching train may be felt for several 
miles. Simple facts such as these teach us that the shock of a fractured 
and falling stratum might be felt over a wide area. The earthquake 
that nearly destroyed the city of Charleston in 1886 was felt over the 
entire eastern half of the United States. 

Earthquakes usually occur in the neighborhood of 
volcanoes and are caused by the tremendous explosions 
which result from formation of steam within the hot 
craters. An earthquake shock may, however, occur any- 



56 PHYSICAL GEOGRAPHY 



where. It may be caused by the breaking or falling of 
rock layers within the earth. Let us suppose that the 
interior of the earth is still cooling and shrinking while the 
cold and rigid crust remains firm. After a time a part 
of the unsupported crust drops down to fill the space left 
through the shrinkage of the interior. The result is an 



Fig. 52. Destructive effects of the earthquake at Messina. 

earthquake shock. If the fall of the stratum is no more 
than a fraction of an inch, the force of the shock may be 
felt for hundreds of miles. Again, suppose that a layer of 
rock perhaps many miles below the surface, is forced 
upward by pressure until it breaks. As the solid earth 
transmits motion easily, such a shock may pass entirely 
through it, and be felt on the other side. 



EARTHQUAKES AND VOLCANOES 57 

Destructive Effects of Earthquakes. The most violent 
effects of earthquakes are felt directly over the focus, or 
seat of disturbance. From this point the shock travels 
outward in circles, diminishing in violence with the distance 
from the focus. The vibration of the earth's crust, pro- 
duced by an earthquake, though slight, is often so sudden 
and violent as to do great damage to human life and 
property. Whole cities are frequently destroyed or greatly 
damaged, as in the case of Lisbon, Charleston, San Francisco, 
Messina, and other places. Great fractures sometimes 
are opened at the surface, followed by eruptions of hot 
water, mud, and sand. Sometimes the vibration has 
a slightly twisting motion, which is especially destructive. 
An earthquake under the sea is sometimes accompanied 
by a tidal wave which rolls inland, destroying everything 
in its course. Among mountain regions great masses of 
rock are sometimes loosened by earthquake shocks, result- 
ing in land-slides, the obstruction of streams, and the 
loss of life and property. 

The countries of the world most visited by earthquakes are Italy, 
Japan, Greece, South America, Java, Sicily, and Asia Minor. Violent 
earthquakes, however, have occurred in other places. On April 18, 1906, 
an earthquake occurred in the city of San Francisco, lasting one minute 
and five seconds. It was caused by the displacement of strata, resulting 
in extensive faults running parallel with the coast. The business 
portion of the city was almost entirely destroyed. Buildings were 
thrown down, railroad tracks were twisted, ridges of earth thrown up, 
and fissures and cracks appeared in the pavements. In some places 
the ground sunk a distance of six feet. In December, 1908, an earth- 
quake destroyed the cities of Messina, Reggio, and a dozen neighboring 
towns and villages. Probably 100,000 persons were killed. No other 
earthquake so destructive of life and property has ever been known. 

Hot Springs and Geysers are formed by underground 
waters coming into contact with the heated rock within 
the earth's crust. When the water flows out of the earth 



58 



PHYSICAL GEOGRAPHY 



steadily it is called a spring; but when it gushes out at 
intervals it becomes a *' geyser." Geysers are found in 
the Yellowstone park and in the islands of New Zealand 
and Iceland, while hot springs are common in all parts of 




Fig. 53. Geysers in Yellowstone park. 

the world. One interesting geyser in Yellowstone Park is 
called "Old Faithful." It spouts a mass of hot water 100 
feet into the air every 65 minutes. Another geyser, known 
as "The Minute Man," erupts every few minutes. 

REVIEW. I. What is the evidence of the internal heat of the earth? 2. What is 
the effect of pressure upon the interior.'' 3. In what regions are volcanoes most numerous.'' 
4. Describe the volcano of Stromboli. 5. Give instances of volcanic eruption. 6. What 
is the cause of hot springs and geysers? 7. What is the cause of earthquake shocks? 
8. Why are they so extensively felt? 9. Describe some of the destructive effects of 
earthquakes. 10. In what countries are earthquakes most frequent? 



CHAPTER X 



EROSION AND GLACIATION 



Erosion and Trans- 
portation. Everywhere 
upon the earth the land 
is being worn down by 
the action of various 
forces, and the worn- 
out materials are 
carried away to fill the 
lower parts of valleys 
and to build up the 
bottoms of lakes and 
oceans. The wearing- 
down process is called 
denudation, or erosion. 
It is accomplished by 
the atmosphere, the 
waters, by heat and 
cold, and even plants 
and animals share in 
the work. The trans- 
portation of the worn- 
out materials is 
accomplished by mov- 
ing waters, the winds, 
and the force of gravi- 
tation. 




Fig. 54. A rocky bluff in Oregon. Notice the 
soil and vegetation on the summit of the rocks. 
The sides of the rock show the effects of weathering. 



59 



6o 



PHYSICAL GEOGRAPHY 



Weathering. If we compare the surface of a freshly- 
broken rock with one that has been exposed to the elements, 
we may notice that the former is hard, shining, and com- 
pact, while the latter is 
dull in color, perhaps 
furrowed with minute 
crevices, and coated 
with loose grains which 
may easily be scraped 
off. This difference 
has been brought about 
by the action of the air 
and moisture, a process 
called weathering. 

A piece of iron left 
in the open air soon be- 
comes red with rust. 
The rust is washed off 
by the rain and carried 
away by the moving 
water. The rusting is 
caused by the oxygen 
of the air, which com- 
bines with the iron to 
form a new substance 
called oxide of iron. 
This process is called 
oxidation. Oxygen will combine with nearly everything 
of which the earth is made. It attacks the surface of 
rocks and loosens the grains which compose them. These 
are washed away by the rain, or fall by their own weight. 
Effects of freezing. Water will soak into the hardest 




Fig. 55. Erosion by a mountain stream. 



EROSION AND GLACIATION 



6i 



rocks, and the seams and cavities with which the)^ abound 
allow it to enter to a considerable distance. When water 
freezes it expands with irresistible force. Fragments are 
in this way torn from the surface of rocks, and even huge 




Fig. 56. Sand dunes in Arizona. 

cliffs are forced apart and the pieces tumbled down. Rock 
expands when heated and contracts when cooled. 

Sudden changes of temperature, such as occur in dry 
regions, cause a corresponding contraction and expansion 
of the rocks which splits off thin scales and small grains 
from the surface gradually reducing them to sand. Plants 
like the ivy and lichen, bushes, and small trees, strike 
their roots into the crevices of the rocks, gradually forcing 
them apart and aiding in the work of erosion. 

At the base of a cliff one may often see a sloping pile of 
rock waste, which has gathered as the result of the agencies 
of erosion. Such an accumulation is called a talus. In dry 
regions, where loose sand is abundant, the winds help along 



62 PHYSICAL GEOGRAPHY 



the work by blowing the sharp grains against the rocks. 
In Arizona the windows of houses are changed into ground 
glass by the sand, and telegraph poles have to be sheathed 
in metal to protect them from its cutting effects. Along 




Fig. 57. Crooked Creek in Long Valley, California. A narrow alluvial plain has been 
formed along the creek. 

sea shores and lake shores the sand is often blown inland 
and piled up in ridges called "sand-dunes." The Bermuda 
islands are largely formed of the ground up shells and sand 
which the wind has carried inland from the sea beaches. 
Along the shores of lake Michigan, the sand-dunes some- 
times bury forests in their progress. 

The work of the winds in grinding up rock waste and in the forma- 
tion of sand hills is especially noticeable in the desert, where there is 
no vegetation to protect the surface. The periodical winds that sweep 
over the Sahara drive the sand along over the stony ground, reducing 
it to the finest dust and increasing its amount by wearing away the 
coarser material. The vast sand hills west of Egypt which continually 
encroach on the fertile Nile valley are blown up by the wind. 



EROSION AND GLACIATION 



63 



The Work of Streams. The rock waste formed by 
erosion is taken up and carried onward by moving waters. 
Every rain-storm washes it farther down the hills, until it 
is caught in the current of 
some swollen rivulet. At last 
the muddy rivulet joins a larger 
stream, which finds its way to 
the river and thence to the 
ocean. Clear water flowing 
through a nearly level channel 
does little in the way of erosion, 
but where the slope is steep the 
stream carries along stones of 
considerable size, the effect 
of which is most important. 
Rough fragments of rock and 
angular pebbles are whirled 
along by the swift current, 
ground together, and worn 
smooth by the friction. The 
bed and banks of the stream 
are deepened and widened by 
these sharp-cutting instru- 
ments, and a fresh mass of 
material is added to the load 
already carried by the swift 
current. By means such as 
these, deep valleys, gorges, and 
canyons have been cut out by 
streams, even hard rock offer- 
ing little resistance to their Fig. 58. The meanders of the 
, J XT 71 - 1 Mississippi showing lagoons or aban- 

tremendous power. When the doned channels. 




64 



PHYSICAL GEOGRAPHY 



stream reaches a lower level and the force of the current 
diminishes, the coarser material is dropped, and only the 
finer waste is carried forward by the slowly moving waters. 
River Valleys. Every valley is the work of the stream 
that flows through it. A swift stream will cut a deep and 
narrow valley. But where the slope is gentle, and the 
stream is fed by heavy rainfalls and melting snows, it may 
overflow its banks in flood time and thus build up an 
alluvial or flood plain. By repeated overflows and succes- 
sive deposits of sediment in the channel and near the banks, 
a river bed may be raised higher than the rest of the plain 
through which it flows. In such cases a part of the stream 
will at flood time often break through the banks and form 
a new channel. This process may be repeated many times, 
until, as in the case of the Mississippi river, a number of 
side streams, or bayous, are formed. 

Deltas. The finer part of the waste carried by rivers 
finds its way to the sea or lake into which the stream flows. 

Here the force of 
the current is 
checked by the 
still waters, and 
the sediment is 
dropped to the 
bottom. In this 
way a large river 
will build up at 
its mouth a de- 
posit called a 
delta. When the 
deposit begins to 
block the mouth 



MEDITERRAN 




Fig. 59. The delta of the river Nile. 



EROSION AND GLACIATION 



65 



of the river, the stream will frequently divide into two chan- 
nels, one on each side of the delta. Each of these streams 
may form a new delta and again divide, forming four chan- 
nels. This process may continue until a dozen or more 
mouths, or distributaries, are formed (Fig. 59). 




Fig. 60. A salt cavern showing stalactite and stalagmite formation. 

Underground waters perform an important part in the 
work of erosion. A large part of the rain-water sinks into 
the earth. It filters through the soil to the rocks below, 
where it finds passages and channels which may lead it 
for many miles before coming again to the surface. In 
the course of its journey it dissolves many substances 
from the soil and rock through which it passes. Lime, salt, 
sulphur, and iron are the commonest of these. When 
the underground stream meets a layer of rock or clay, 
which is waterproof, it flows along until it emerges at the 



66 



PHYSICAL GEOGRAPHY 



surface as a spring. If the spring contains minerals in 

solution it is called a mineral spring, and may be useful as 

a cure for certain diseases. If the water happens to pass 

over heated rock it may come to the surface as a hot spring. 

Caverns are formed in limestone rock because it is easily dissolved. 
In some regions where this is the prevailing rock the entire drainage is 




Fig. 6i. Glacier and lake among the Alps. 

underground. The water dissolves out passages many rniles in extent. 
These widen and deepen into great chambers, and the streams flowing 
through them are really subterranean rivers. Where the water filters 
through the roof of the cavern, it evaporates, leaving great pendants of 
limestone, which resemble icicles. Where the water drops upon the 
floor of the cave, masses of lime are built up, called stalagmites. These 
sometimes meet the stalactites hanging down from above and the two 
together form a column extending from the floor to the roof of the 
cavern. The Mammoth Cave, in Kentucky, and the caverns of Luray, 
in Virginia, are the most noted of these natural curiosities. 

Glaciers are streams of ice which flow through the valleys 
in high mountain regions. The snow that falls upon the 
mountain tops in such regions, slides down into the valleys, 
where it accumulates until the valley is filled from side to 
side. Here some of the surface snow melts, and the water, 



EROSION AND GLACIATION 67 

filtering through the rest of it, aided by the increasing 
pressure from above, changes the whole mass to ice. This 
ice stream moves down the valley from one to two feet 
per day. It carries along with it all the loose rock material 
which it finds on the bottom and sides of the valley. The 
waste formed by weathering, and the loosened stones and 
boulders that fall upon it are carried miles down the valley. 




Fig. 62. A glacier in Alaska entering the sea. 

When the front of the glacier reaches the lower and warmer 
part of the valley, the ice melts and becomes the source 
of a stream. The rock waste left behind in a mass of earth 
and stones at the end of the melting glacier is called a 
terminal moraine. The waste deposited along the sides 
forms lateral moraines. If two glaciers coming from dif- 
ferent valleys happen to join, there will be a third moraine 
in the center. This is called a medial or middle moraine. 
The rocks and boulders imbedded in the bottom and sides 
of the glacier are scratched and polished by rubbing against 
the cliffs along which they pass. 

Glacial Drift is the name given to the waste left by the 
melting- glacier. The finer part of it is carried away by 



PHYSICAL GEOGRAPHY 



the water that comes from the melting ice, and spread out 
over the lower valley, and is taken on to the sea by the 
rivers. 

The antarctic regions and Greenland are entirely covered 
with thick ice caps. As the ice moves down to the ocean, great 

masses break off and 
float away as icebergs. 
Some of them are truly 
"ice mountains," being 
more than a mile from 
top to bottom. They 
float into warmer 
waters, where they 
melt and drop the load 
of earth and stones 
which they carry. It 
is thought that the 
fishing banks off the 
Newfoundland coast 
were partly built up in 
this way. 

The Great Ice Sheet of North America. Much of the 
northern part of the United States and a great part of 
Canada are partially covered with a great sheet of glacial 
drift. This sheet varies in thickness from a few feet to 
several hundred, and contains rocks and boulders that 
must have come from regions far to the north of their 
present position. Masses of copper and red jasper boulders 
are found in Indiana that were brought down from the 
shores of lake Superior and lake Huron. In southern 
New England the boulders appear to have come from the 
Green mountains to the northwest. A study of the glaciers 




Fig. 63. A huge boulder left balanced on a cliff 
by the glacier. 



EROSION AND GLACIATION 



69 



of the Alps long ago convinced scientific men that the drift 
that now overspreads northern America and northwestern 
Europe was brought there by moving masses of ice. The 
scratches upon the rocks point toward the region of Hudson 
Bay as the origin of the glaciers. 

Cause of the Glaciers. It is supposed that the section 
where the glaciers originated was raised by movements 
of the earth's crust to such a height that the climate became 
as cold as that of the polar regions is now. The ice ac- 
cumulated to a great depth, and moved down from the 
elevated regions in every direction. The tops of moun- 
tains were broken off and smoothed down, deep valleys 
were plowed out, streams were dammed by the huge 
mountains of moving ice. The soil, gravel, rocks, boulders, 
and waste of every sort were pushed along by the bottom 




Fig. 64. Chart showing the southern limit of the great North American glacier. 
The arrows indicate the direction in which the glacier moved. 



70 



PHYSICAL GEOGRAPHY 



of the glaciers. It was like a great sheet of rough sand- 
paper dragged over the surface of the earth, and pushing 
along all the fragments loosened by its friction. When 
the front of the glacier reached lower latitudes, it began 
to melt and deposit its load of drift. 

Limit of the Glacier. The map (Fig. 64) shows the 
limit reached by the glaciers in the United States. Along 
this line are found all 
the debris of a termi- 
nal moraine. Connec- 
ticut, New York, 
Ohio, and all the states 





Fig. 65. Glacial lakes in New Englanc 



along the glacial front 
are strewn with huge 
boulders that were 
smoothed, scratched, 
and rounded on the 
long journey. 

Results. When, after many thousand years, the ice 
melted, the valleys and troughs scooped out by the glaciers 
were filled with water and became lakes. The lakes of 
central New York occupy valleys that were thus deepened 
by the ice. It is thought that the melting of the ice was 
due to a general lowering of the surface over which it had 
spread. As this took place very slowly, the front of the 
glacier in its slow retreat continued to strew the ground with 
soil from its terminal moraine. The fertile farming lands 



EROSION AND GLACIATION 



71 



of the lake regions and the middle west are due to the rich 
deposits left by the glaciers. 

The glaciated regions of Europe are similar to those of 
North America. The ice spread from the Scandinavian 




Fig. 66. Crossing a glacier among the Alps. 

peninsula as a center. It filled the North and Baltic seas 
and reached well into central Europe before melting. 

REVIEW. I. What is meant by erosion.'' 2. How is it accomplished.? 3. What 
are the agencies of transportation? 4. Tell something about each. 5. Explain what is 
meant by weathering. 6. How is it effected.'' 7. Describe the effects of oxidation and 
freezing on rocks. 8. How do plants help the work of erosion? 9. Describe a talus. 
10. What finally becomes of it? 11. Tell how winds accomplish erosion. 12. \\'here 
are the winds most effective? 13. Describe the work done by moving water. 14. How 
have valleys been formed? 15-. Describe the growth of a valley. 16. How are deltas 
formed? Name some rivers which have deltas. 17. What part do underground waters 
take in the work of erosion? 18. Explain how caverns are formed. 19. Stalactites and 
stalagmites. 20. What are glaciers? 21. Describe their erosive action. 22. Different 
kinds of moraines. 23. What is glacial drift? 24. How are icebergs formed? 2;. De- 
scribe three effects of glaciers. 26. The North American ice sheet: its cause, location, 
and effects. 



CHAPTER XI 



THE WATERS OF THE LAND 

The ocean is the original source of all the waters of the 
land. The rising vapor blown over the land surface is 
transformed into the falling rain and the various forms of 
precipitation. The rain, the frost, the ice, and the atmos- 
phere, through their work of erosion and transportation, 
have diversified the surface of the continents with hill, 
valley, mountain, and plain, and fitted them for the 
dwelling place of man. 




Fig, 67. Gorge of the Niagara river. 
72 



THE WATERS OF THE LAND 73 

Drainage Systems. When rain first began to fall upon 
the bare rocks of the new-formed continents, it ran off 
swiftly in sheets and streams. There was no soil or plant 
life to retain the water, and therefore no springs nor per- 
manent streams. At first the floods of rain would flow off 
in a single stream between two adjacent ridges. As this 
stream cut its channel deeper and deeper into the rock, 
side-streams began to carve out channels for themselves. 
The land gradually became deeply cut by numerous swift 
torrents. After a time the main stream would cut its way 
down to the ocean level. Its speed would then slacken 
and the deposit of sediment would begin at the mouth. 
And as the channel gradually deepened inland, the current 
continued to slacken, and the load of waste was deposited 
farther and farther up stream. As a result of the filling 
up of the channel, it became too small to carry the water 
during the rainy season. The river would then overflow 
at flood time and the sediment deposited would begin the 
formation of an alluvial plain. 

During this time the hills and mountains were being 
worn down by erosion. Streams gnawing at their bases 
carried off the waste. The flood plain crept farther up 
the stream, until the smaller streams also began to widen 
their valleys. At last only the hard part of the mountains 
remained projecting above the plain. All the rest had 
been worn to fragments and spread out along the courses 
of streams or carried down to the ocean. 

Results. Thus in changing old land into new land, a 
drainage, or river, system has been built up. Fertile soil 
has been prepared for agriculture and for the homes of 
men. Mountain torrents have become quiet streams, 
suitable for navigation. The growth of vegetation has 



74 



PHYSICAL GEOGRAPHY 



kept pace with the deepening of the soil and the hills and 
valleys are clothed with forests and varied forms of plant life. 
Watersheds and Basins. If any stream be followed to 
its source, it will be possible to find, in the near neighbor- 
hood, water flowing in another direction. The ridge 
lying between two stream sources is called a watershed, 
or divide. Such divides can be traced along the head- 
waters of all streams. All the land that is drained into a 




Fig. 68. Rapids in a river used for obtaining power. 

single river is called a basin, and the main stream with all 
its branches a river system. 

One of the largest river basins in the world is that of 
the Mississippi. It drains nearly one half of the area of 
the United States, and carries to the gulf of Mexico every 
year enough sediment to cover a square mile of surface to 
the depth of 270 feet. Its delta covers an area of 10,000 
square miles. Each one of its thousand tributaries has its 
own watershed and basin, and is carrying on the work of 
erosion and transportation. 



THE WATERS OF THE LAND 



75 




Fig. 69. Spring on a hillside. The hill is cut 
through, showing layers of porous rock at A and 
layers of clay at B. 



Lakes are bodies of water that fill depressions in the land. 

Some of these depressions were made through movements 

of the earth's crust; a far greater number were scooped 

out by glaciers. Lakes are most common in mountain 

regions. Many little 

valleys are surrounded 

by a rim of hills, and 

the drainage water 

pours into these valleys 

until they are full. At 

the lowest point in the 

bordering hills the 

overflow will break 

through, and the lake 

becomes the source of 

a stream. 

Salt Lakes. Much of the water of a lake is evaporated 

by the sun. The springs and streams that feed it contain 

salt and other minerals in solution. When such water 

evaporates, the min- 
erals are left behind. 
If more w^ater flows 
into the lake than is 
carried off by evapora- 
tion, there must be an 
outlet, and the water 
will remain fresh; but 
if the evaporation is 
equal to water received 
by the lake, the amount 
of salt contained in the 

Fig. 70. Section of the earth showing how water 11 -ii ',^^-^00^ ^ud 

is supplied to a weU. The rock at C is waterproof, iake \\iU mcrease ana 




76 PHYSICAL GEOGRAPHY 

its waters will become salty. In many cases such lakes have 
dried up entirely, leaving a bed of salt behind. From one 
such lake bottom, in the Caspian sea region, 100,000 tons 
of salt are annually removed. The salt lakes found in 
central Asia and in some regions of Africa are arms of the 
sea which have been cut off by the rising of the land. Such 



Fig. 71- Sectional view of rock strata, illustrating basin shape and source of an 
artesian well. 

lakes are slowly drying up. The desert of Gobi is the bed 
of a dried-up lake. 

"Wells and Springs. The origin and work of springs have 
been mentioned (Fig. 69). A well is obtained by digging 
or boring down into the earth until strata are found that 
carry water. Such strata are said to be "permeable." 
If they are underlaid by "impermeable" strata, the water 
will be held until it can find an outlet. If a permeable 
stratum slopes from a higher to a lower level, it may furnish 
an artesian well. A boring is made into the earth deep 
enough to strike the water-bearing rock. As fast as the 



THE WATERS OF THE LAND 



77 



boring is made, iron pipe is driven down, through which the 

water rises. If the outcrop of the water-bearing rock is 

higher than the well, the water will flow; if it is lower, the 

water must be pumped out. 

The basin shape of the continents is favorable to the foundation 
of artesian wells. In the interior of AustraHa and in parts of Africa 
and the United States the7 are often the only source of water. Many 
cities obtain part of their 
water from Artesian wells. 
The water is often so cold 
that no ice is required in 
the hottest weather to make 
it agreeable for drinking. 

An intermittent 

spring is one that flows 
for only a short period 
at a time. Its action 
may be understood 
from Fig. 72. When 
the water rises to the 

1 . 1 , r ^1 Fig. 72. Intermittent spring showing siphon outlet. 

highest part of the ^ ' 

bend in the outlet the water flows. It will continue to 
flow until the level falls below the outlet. The spring will 
then stop until the level rises again. 

Relation of Rainfall to Land-Surface and Vegetation. 
It is clear that the amount and value of the waters of the 
land depend on rainfall. The erosive power of rain and 
streams depends on the amount of water that acts. Whether 
vegetation shall be luxuriant or scanty, depends also on the 
amount of rain received. Where the rains are too heavy, 
a flood plain like that of the Amazon may become a swampy 
jungle of little value to man. Where the rainfall is too 
little, as in the case of the western plains of North 
America, vegetation is scanty, crops fail, and flocks and 









^ ^^ 


/^^^^^ 


1^ 


^ 




11 fi/t 

I'm 


■ 


■ 


1 


^ 






c 


=< 


^ 


■ — ""^s^p^ 


^VVxVy 




B 


■ 


» 



78 PHYSICAL GEOGRAPHY 

herds often starve. A moderate amount of rain at frequent 
intervals brings the most satisfactory results. The rivers 
flow to the sea and return to the earth again, keeping it 
suitable for the abode of man. 

REVIEW. I. Explain how the ocean is the source of the waters of the land. 
Describe the development of a drainage system. 2. How were flood plains formed.? 3. 
Define watershed; river basin; river system. 4. Tell how lakes have been formed. 5. Why 
are some lakes salt.'' 6. Describe an artesian well; an intermittent spring. 7. How is 
rainfall related to the surface of the land apd to vegetation? 



CHAPTER XII 



ISLANDS 

Classes. About eight per cent of the land surface is 
composed of islands. The most of them are found near the 
shores of the continents and are called continental islands. 
The others lie far out in the oceans, surrounded by deep 
water, and hence are called oceanic islands. Oceanic 
islands are divided into coral and volcanic islands, accord- 
ing to their origin. 

Continental Islands are thought to have once been 
joined to the continents near which they lie. There is 
much evidence to support this theory. The plants and 
animals of both are of the same species. The seeds of 
plants might 
have been car- 
ried across 
straits of con- 
siderable width, 
but land animals 
could not have 
passed from the 
mainland to 
these islands un- 
less they were 
connected. The 
rocks of the con- 
tinents and 
those of the 




Fig. 73. Continental islands near the coast of Maine. 
The island chains have the same general direction as the 
Appalachian Mountain system. 



79 



8o 



PHYSICAL GEOGRAPHY 



neighboring islands are similar. The coasts of England 
and France, on opposite sides of the straits of Dover, are 
formed of chalk, a kind of limestone, and the straits are 




Fig. 74. Atoll formd by the sinking of a volcanic island. 



not more than 300 feet deep, indicating that these coun- 
tries were separated by a sinking of the land. 

Continental islands appear to have been formed by a sinking of 
the coasts of the continents. They are usually arranged in lines 
parallel with the coast, or connect projecting parts of the coast. The 
chain of the West Indies connecl^s the coast of Venezuela with the 



ISLANDS 



8i 



southern extremity of Florida. The Japan islands and the Philippines 
form a continuous chain from Kamchatka to the southern coast of 
Asia. It seems as if a rugged coast had sunk, leaving only the tops 
of the mountains projecting above the water. The southern end of 
Kamchatka is connected by the chain of the Aleutian islands with the 
Alaska peninsula. 

Volcanic Islands are plentifully scattered through the 
southern part of the Pacific ocean. Several groups are 
found off the coast of Africa. Iceland and the Hawaiian 
islands are the most extensive of this class. Many con- 
tinental islands 
also, as for ex- 
ample Japan 
and the Lesser 
Antilles, are 
volcanic. 

Volcanic islands 
are sometimes 
formed suddenly of 
lava and cinders 
thrown up from 
the ocean bottom. 
They sometimes 
disappear soon 
after forming. 
Some volcanic 
cones have been 
ringed with coral 
and made into 
atolls. 

Coral Islands are built by a minute animal called the 
polyp, aided by the winds and waves. The coral polyp 
flourishes in warm, shallow sea-water containing a little 
sediment. It has the power of extracting lime from the 
sea-water and building it up in the form of coral. Some 
of the coral consists of solid masses; other kinds are branch- 
ing like a tree. White is the usual color, but some is of a 



' f_ 


' i/ 


•5^^ 


^ 


^ 


§1^^ 




^^S 


"^ 




^. 


^ 




^tL 


' . -.w^^sSJ^^^^W****^ 


1 



Fig. 75. Flower-like polyps building up a branch of coral. 



82 



PHYSICAL GEOGRAPHY 



light red and is much used for jewelry. One of the beauti- 
ful sights among the Bermuda islands is the coral groves 
seen through the clear water. The sea bottom seems to 
be covered with red and white branching trees, while 
fishes, brilliant in scarlet, yellow, green, and gold, dart 
hither and thither among the branches. 

The work of the polyp consists in the building of reefs near the 
shores of continents and islands. If the reef is close to the shore, it 

is called a fringing reef, but 
if at a distance, a barrier reef. 
There is a great barrier reef 
off the coast of Australia 
1,200 miles long. The sea 
between a reef and the shore 
is smooth and in places forms 
a good harbor. 

The atoll is a curious cir- 
cular reef built by the polyp 
around the crater of extinct 
submarine volcanoes, or off 
the shore of an island which 
has afterward sunk. 

A barrier or fringing 
reef would be changed 
into an atoll by a slow 
sinking of the island 
around which it is built. 
During the sinking, the 
Fig. 76. Red coral formation. ^oral is all the time 

growing, so that in time there would be a ring of coral sur- 
rounding a shallow lake. This coral ring is the foundation 
of the atoll. The drift of the sea lodges among the branches; 
the pounding surf breaks off pieces of coral which fall into 
spaces below and help to bring the reef above the water. The 
seeds of plants are borne to the reef by the winds and waves. 
They take root and grow and add their remains to the 




ISLANDS 83 

rising mass. Finally, when palm-trees begin to flourish 
and there is fruit enough to support life, men come to 
make their homes on the atoll. 

REVIEW. I. Name the three classes of islands. 2. Location of continental islands. 
3. What is the evidence that they were once a part of the continents? 4. Name the 
chief groups of continental islands. 5. What is the origin of volcanic islands.? 6. 
Describe the growth of coral islands. 7. Atolls, fringing and barrier reefs. 



CHAPTER XIII 

THE COAST LINE 

Importance. Nothing is more important to a com- 
mercial country than the character of its coast line. The 
great increase in ocean traffic and the size and draft of 
modern vessels make it necessary to have deep harbors 
and to take precautions against dangers from the shoals, 
sandbars, rocks, and reefs, which are found on every 
coast. The care of the coast is given to the general govern- 
ment. The United States Coast Survey provides charts 
of the coasts, showing the depth of waters and the accurate 
location of every coast feature of importance to naviga- 
tion. Many millions of dollars are spent each year in 
deepening channels and harbors, and in building break- 
waters and jetties to keep them clear and safe. Light- 
houses and signals are built on dangerous coasts, and bell- 
buoys and lightships are anchored over hidden reefs. 
Each port has its trained pilots to conduct ships safely 
into the harbor, and life-saving stations are established 
along the coast to rescue those who have suffered ship- 
wreck. 

Changes in the coast line are always in progress. Some of these 
are the work of the restless ocean itself; others are the result of the 
rising or sinking of the land. The sediment brought down by the 
rivers may form sandbars at their mouths, or may be dropped farther 
off shore, to be afterward raised up in the form of island barriers. 
The ocean floor near the coasts of continents is thickly strewn with 
the deposit of rivers. This sediment builds up a plain beneath the 
waters. A rising of the coast would bring this plain above the surface 
as a coast plain. The sediment which has been deposited assumes a 
variety of forms. Some of it is shaped into long lines by the movement 



THE COAST LINE 



§5 



of the ocean waters; other forms are delta-shaped, with the longest side 
toward the ocean. 

The southern part of the Atlantic coast of North America, 
after a long period of rising, is slowly sinking again. Its 
rising brought the ocean floor to the surface as a coast 
plain, and quickened the flow of rivers, which cut deeper 
channels and brought down a 
larger amount of sediment. 
The results of sinking have 
been the formation of swamps 
and marshes along the coast 
and the deepening of the 
mouths of rivers. When the 
bed of a river sinks below sea 
level it is called an estuary, or 
drowned valley. The Thames 
and the Hudson rivers are 
examples of drowned valleys 
that are excellent harbors. 
The Atlantic coast plain in- 
creases in width from New 
York all the way to Texas, 
but from the north to south 
it is increasingly flat and 
swampy and the sinking has 
not yet progressed far enough 
to make good harbors. 

An interesting proof of the sink- 
ing of the coast is furnished by the 
buried cedar forests along the 
New Jersey shore. Every traveler 

along the Pennsylvania railroad has p.^_ ^^_ ^ p^^^ ^^ ^j^^ ^^^^^ ^^ ^^^ 

noticed the stumps and logs lymg jersey, showing islands and beaches 
in the marshes. The cedar grows formed from sand. 




PHYSICAL GEOGRAPHY 



only on high ground. Hence the coast must have been once raised 
many feet above its present position. 

Fiords. Along rocky shores, where the mountain ranges 
make an angle with the coast, the sinking of the land allows 
the sea to flow up the long, narrow valleys, forming fiords. 
These are numerous along the coasts of Norway, Alaska, 




Fig. 78. A fiord on the coast of Norway. 

and the southern half of Chile. In Scotland they are 
called firths. Where the tide rises to a considerable height, 
it flows back and forth through these long inlets, making 
them deeper and wearing away the softer parts of the rocks, 
often cutting them into curious and fantastic forms. 
Caverns of great beauty are often carved out. The dash 
of the waves and currents carries off the worn-out material, 
often leaving pillars of hard rocks known as "stack." 
Effect of Waves and Currents. The ceaseless dash 



THE COAST LINE 



87 



of the waves and currents against the shore and the grind- 
ing up of the rocks and pebbles by the surf form a vast 
quantity of sand in addition to the sediment brought down 
to the sea by rivers. This 
mass of fine, worn-out matter 
is shaped by the currents 
which sweep along the shore 
into various forms. Where 
the river empties into a sea 
that has no currents, a delta 
is made. But in most cases 
the currents are stronger than 
the rivers; then the sand will 
be piled up in a long bar 
across the river's mouth. Or 
if the direction of the ocean 
currents is parallel with the 
shore, the silt will be swept 
away from the mouth of the 
river and spread out in long 
lines along the coast. Some- 
times a bar will be formed, 
partly closing a bay; it is then called a spit. Occasionally 
by the action of two currents it is bent in the form of a 
curve or hook; it is then known as a hook, or hooked spit. 

REVIEW. I. What is the value of the coast line? 2. What provisions are made for 
the safety of ships? 3. Describe some changes always in progress along the coast? 
4. Rising and sinking coasts and proofs. $. What are fiords? 6. Describe the forma- 
tion of sandbars, as to origin and deposition of the sand. 7. Peculiar forms of bars. 




Fig. 79. Cape Cod, a hook formed 
from sand through the action of the tides 
and waves. 



CHAPTER XIV 

THE SEA 

General Description. The sea is the continuous body 
of salt water surrounding the globe and enveloping the 
land masses on every side. The continents make four 
divisions of it which we call oceans. The Pacific ocean is 
nearly equal in size to the other three, and is the deepest, 
averaging 2^ miles. The deepest sounding ever made 
was 31,600 feet, near Guam. The ocean bottom is nearly 
a continuous plain. There are gentle elevations and 
deep depressions, but it has been said that a railroad could 
be run around the world on the ocean floor without any 
grading. This fact makes it easy to lay down telegraphic 
cables, so many of which no)5^ stretch across the ocean 
floors in every direction. The sediment from the rivers 
does not reach far beyond the borders of the continents, 
but the greater part of the ocean bottom is overspread 
with the remains of plants and animals which have sunk. 

The greater part of the sea is open to navigation, but the 
regions around the poles are filled with floating ice. This 
ice helps to keep the waters cold, but prevents free naviga- 
tion in those parts. The icebergs that break from glaciers 
and float away with the ocean currents are among the 
dangers that beset the sailor. The sea level is taken as 
a standard by which to measure the heights of the land and 
depths of the sea. When we speak of a mountain 5, 000 
feet high, we mean so many feet above the sea level, and 
not that the top is 5,000 feet above the base. 



THE SEA 



89 



Temperature and Pressure. The temperature of the 
ocean depends on latitude and depth. The deep waters 
vary only slightly from the freezing point, being 29° in 
the polar regions and 35° at the equator. The heating 
effects of the sun do not reach lower than 600 feet, and the 
waves and tides that disturb the surface do not affect the 
water below a depth of 100 feet. The temperature of the 
surface waters varies from 80° F. at the equator to a freez- 




Fig. 80. An iceberg off the Coast of Newfoundland. 

ing temperature at the poles. The salt of the sea makes the 
water a little heavier than fresh water. One hundred 
pounds of sea water contains 3^ pounds of mineral matter, 
the most of which is common salt. It is thought that sea 
water has been salt from the beginning; but it must be 
growing more and more salt because vast quantities are 
carried into it every year by rivers. 

Pressure in the depths of the sea is very great. At a 
depth of two miles, it is two tons to the square inch. 
Since the density of water does not increase with depth, 
the pressure at a depth of one mile would be one ton per 



90 



PHYSICAL GEOGRAPHY 



square inch. The pressure of the air upon our bodies is 
15 pounds per square inch. At a moderate depth it would 
be impossible for a human being to live. When deep-sea 
fish are brought to the surface they are killed at once by 
the change of pressure. Their bodies crack open and 
their eyes bulge out. 




Fig. 81. Wave motion caused by striking a line. C D equals height of wave; A B 
equals length of wave. 

Movements of the Water. Water is easily set in motion. 
The lightest breeze upon its surface will cause a vibratory 
movement. A jar or shock within the earth's crust, 
such as may accompany an earthquake or a volcanic 
eruption, will cause waves of extraordinary height and 
destructive force (page 57). It is almost proverbial that 
water is never at rest, and the sounds which one may hear 
by the sea are infinite in number and variety. You may 
not be able to detect any cause for the motion of the sur- 
face of the water or of the surf and breakers which strike 



THE SEA 



91 



against the shore, for the disturbing force may be many 

miles away. 

_ Fill a pail with water and strike a slight blow against the bottom or 
side and notice the effect on the water. Throw a stone out into a 
pond or pool of water and observe the effect. 

Waves, Breakers, and Surf. Waves consist of an up- 
and-down movement of the surface of the water, caused 




Fig. 82. Breakers forming near the shore 

by the winds which are continually blowing against it. 
The varying pressure of the wind causes the water to 
vibrate with a slight motion backward and forward, but 
there is no onward movement of any mass of water. It 
is merely the wave motion that moves onward, just as we 
may observe it when the wind blows over a field of tall 
grass or grain. The stalks vibrate backward and for- 
ward, but the motion appears to sweep entirely across the 
field. 

We may illustrate wave motion by attaching a cord to hooks on 
opposite sides of a room and drawing it moderately taut. If we strike 



g2 PHYSICAL GEOGRAPHY 



the cord with a stick at one end, a motion resembling that of a wave 
will travel its entire length. The method of measurmg dimensions 
of waves is shown in Fig. 8i. The summit of the wave is_ called its 
"crest" and the bottom of the wave its "trough." The height is the 
perpendicular distance between crest and trough and the length is the 
distance from crest to crest. • , t • i 

The height of waves varies with the force of the wind, in violent 
storms waves sometimes occur fifty feet in height and over a thousand 
feet long with a rate of speed varying from forty to sixty miles per 
hour. Small vessels are frequently swamped by such waves, and even 
the largest steamships are sometimes seriously damaged. 

When waves approach the shore and enter shallow water, 
the front of the advancing crest becomes steeper and steeper 
until it falls forward upon the beach, forming a breaker. 
The foaming water then rolls up farther inland as surf. 
The ceaseless flow of the surf back and forth and the pound- 
ing of the breakers on the beach grind up the pebbles 
and shells into the finest sand. On steeply sloping shores 
the waves strike with great violence, breaking cliffs to 
pieces and sometimes destroying buildings, piers, and 
other structures. 

Tides. Anywhere at the seashore one may observe 
the regular rising and falling of the water level. During 
six hours the water rises farther and farther up the slop- 
ing beaches, or higher and higher on docks and piers, until 
the *'high water" mark is reached. For the next six 
hours the level falls, and we have "low water." On the 
open sea, far from land, the rise of tide does not exceed 
one foot, but at the shore its height varies with the direc- 
tion of the coast line, it being greatest in inlets with con- 
verging sides and least on points and headlands. 

Causes. It was observed many centuries ago that the 
recurrence and height of the tides corresponded with the 
position and phases of the moon. The scientific proof of 
this relationship, however, was the result of the applica- 



THE SEA 



03 



tion of Newton's Law of Gravitation. The tides are 
caused by the attraction of the moon for the mass of water 
forming the oceans. Water being mobile, the hydrosphere 
is drawn out into the form of a prolate spheroid (page 00), 
and as the earth rotates beneath the moon from west to 
east this spheroidal shell of water has an apparent motion 
in the opposite direction. That is to say, the tides travel 
around the earth from east to west once every twenty- 
four hours. As there are 
two "high tides "on oppo- 
site sides of the earth and 
two "low tides" at a dist- 
ance of 90° from these, it 
follows that a high tide and 
low tide will succeed each 
other every six hours. 

As a matter of fact, the suc- 
cession of high and low tides 
requires twenty-four hours and 
fifty minutes to pass around the 
earth. Thus any point at the 
seashore has high tide about fifty- 
two minutes later each day. The 
reason for this may be understoodby study of Fig. 83. While the 
earth is rotating on its axis, the moon is also revolving about the 
earth in the same direction. As the revolution of the moon 
requires about twenty-eight days, it will be overhead on any point of 
the earth about fifty-two minutes later each day. When the moon 
occupies the position M, the points A and B, directly underneath it and 
on opposite sides of the earth, will have high tide. Now, if the moon 
remained at rest, point A would come underneath it every twenty-four 
hours, but during this period the moon has moved onward to W, and 
fifty-two minutes longer are required for points A and B to be brought 
into a straight line with the sun. 

Efifect of the Sun— Spring and Neap Tides. The attrac- 
tion of the sun also causes a tide in the same manner as the 




Fig. 83. Illustrating the cause of varia- 
tion in the recurrence of tides. 



94 



PHYSICAL GEOGRAPHY 



attraction of the moon; but, although the sun is much larger 
than the moon, it is so far away that the solar tides are only 
two fifths as great as the lunar tides. When the sun, the 
moon, and the earth are in the same straight line, as shown 
in Fig. 84, the attractive forces of the sun and moon are 
exerted in the same direction, and the resulting tide is 
known as spring tide. The spring tides occur at the time 
of new moon and full moon. When the sun and moon are 




Neap 



Spring 



Tide 




Fig. 84. Spring and neap tides. 

in the first position shown in Fig. 84, they attract the water 
in directions at right angles to each other, and the result 
is a lower tide than usual, called neap tide. The recur- 
rence and height of the tides are further complicated by the 
variation in the distances of the sun and moon from the 
earth and in the angles which their orbits make with each 
other. The great variation also in the depth of the oceans 
and in the configuration of the coast produces an endless 
variety of tides, and each place has its own conditions 
which must be studied in order to determine accurately the 
time and height of its tide. 



• THE SEA 95 

Effects of Tides. The tides are of service to navigation 
in the periodic deepening of harbors and mouths of rivers, 
thus allowing vessels of greater draft to enter and 
leave port. They help to purify the water by keeping it 
in motion and thus bringing every part of it into contact 
with the oxygen of the air. But the tides also carry sedi- 
ment along the coasts, sometimes depositing it at the 
mouths of rivers and harbors, whence it must be removed 
at great expense and trouble. Where tides flow through 
narrow channels they sometimes form swift and dangerous 
currents, called races, which flow alternately back and 
forth. When the tide enters the mouth of a river having 
a strong current, the water rises in a high mass called a 
bore, which travels up stream with great swiftness, often 
wrecking small vessels and doing damage along the coast. 

Ocean Currents. Not only are the surface waters of 
the ocean disturbed by waves and tides, but the entire 
mass of oceanic waters takes part in a vast and compre- 
hensive system of movements, called currents. By means 
of these currents, the cold waters of the polar regions are 
brought toward the equator, and the warm waters of the 
equatorial regions toward the poles, thus tending to equalize 
both the temperature and saltness of the waters. Through 
this transfer of cold and warm waters, the temperature 
of the winds is also affected and the climate of the lands 
over which they blow. 

The movement of the surface currents of the ocean 
corresponds so nearly with the direction and force of the 
winds that these are considered to be their principal cause. 
Along the equator, for example, the currents have the same 
direction as the trade-winds, flowing westward until they 
are interrupted by the shores of the continents. The 



96 



PHYSICAL GEOGRAPHY 



direction of coast lines is a second important cause of the 
direction of currents, since the water on striking the coasts 
must follow their direction. 

When the north equatorial current (Fig. 85) strikes the coast of 
South America and Asia it is deflected northward, following the trend 
of the coast. After crossing the tropic of Cancer this current becomes 
kriown as the Gulf Stream in the Atlantic ocean, and the Japan Current 
in the Pacific ocean. These currents, on coming into the region of 




Fig. 85. Chart of the ocean currents. 

westerly winds, are bent eastward until their waters strike the shores 
of North America and Europe. On the coast of Europe the Gulf 
Stream divides, part of it passing into the Arctic ocean, and a part 
returning toward the equator. The passage through Bering strait 
being narrow, the entire Japan Current is bent southeastward by the 
western coast of North America, and returns again toward the equator. 
The south equatorial current may be traced in a similar manner 
as shown in Fig. 85. In the Pacific ocean it is deflected southward by 
the coast of Australia, and in the Atlantic by the shore of South Amer- 
ica. As a result, these currents turn to the southeast and join the 
drift or return currents flowing eastward. In the Indian ocean, south 
of the equator, the ocean currents make a circuit, which is much like 



THE SEA 97 

that in the Atlantic and Pacific. An important feature of the cur- 
rents of the Indian ocean is the effect of the periodic winds or monsoons, 
These currents are north of the equator and change their direction twice 
a year, soon after the change in the direction of the winds. This fact 
is accepted as conclusive proof that currents are mainly the result of 
the winds. 

Other Causes. It is no doubt true that ocean currents 
are affected by a difference in the specific gravity of the 
waters, caused by variations in temperature and salt- 
ness, and by the rotation of the earth. The great heat 
and heavy rainfall of the equatorial regions tend to 
make the water lighter. It therefore rises and flows in 
the circuit described above, while the heavier water from 
the colder regions returns toward the equator as deep-sea 
currents. The rotation of the earth would tend to set up 
a flow of currents in the same direction as the winds. 

Counter or Return Currents. The westward trend of 
ocean currents in the regions of the trade-winds tends to 
bring about a return current along the equator in the 
regions of calms. The regions of calms along the tropics 
are marked in each ocean by sluggish westward currents, 
which with the other currents described, form whirls or 
eddies, into which immense masses of seaweed and other 
floating debris of the ocean are drawn, giving these places 
the appearance of grassy seas. 

Effects of Ocean Currents. The chief effects of ocean 
currents are seen in the climate of the bordering coun- 
tries. A study of the chart (Fig. 85) shows that the west- 
ern sides of the oceans are heaped up with water which 
has been warmed by its passage westward across the 
ocean under a tropical sun. The winds that traverse 
these warm waters are necessarily heated and loaded with 
water vapor, resulting in the heavy rainfall of tropical 



gS PHYSICAL GEOGRAPHY 

regions. Again, as these warm waters are distributed, 

they return into the regions of westerly winds, and the 

climate of Europe, the western coast of North America, 

and other temperate countries are supplied with heat and 

moisture. On the eastern shores of Asia and North 

America are cold currents, which descend from the Arctic 

regions, and these coasts are correspondingly cold. The 

cold water, however, is favorable to the principal varieties 

of fish and are the most valuable fishing grounds in the 

world. In the days of sailing vessels ocean routes were 

laid out as nearly as possible along the ocean currents, but 

the influence of these currents is of little importance on 

steam navigation, and the courses of steamships are now 

determined by other considerations. 

The ocean currents from the Arctic regions bring with them vast 
masses of ice in the form of floes and icebergs. Such masses transport 
the stones and soil which they have taken up in their journey across the 
land as glaciers. When the ice melts this material is of course distributed 
over the ocean floor. We thus see that the ocean, by means of its winds 
and currents conveying heat and moisture, and by means of the life 
which it supports, is of the greatest service to mankind. As a high- 
way for vessels it carries the commerce of the world, and its cooling 
breezes and moderate climate are sought by thousands in pursuit of 
health. 

REVIEW. I. Describe the sea, giving its chief divisions, depth, nature of its floor, 
etc. 2. What is said about the sea level? 3. Temperature of the ocean at different 
depths and latitudes. 4. Quantity of salt in the sea. 5. How does pressure vary in the 
sea? 6. Why is it so great? 7. Describe the mobility of water. 8. How is the water of 
the ocean disturbed? 9. What is a wave? How caused? How measured? 10. 
Describe the effect of breakers and surf along the shore. 11. Describe the phenomena of 
the tides seen along the shore. 12. What is the chief cause of the tides? 13. Explain 
their recurrence. Why later each day? 14. Effect of the sun on tides. 15. What is 
the cause of spring and neap tides? 16. Describe the effects of the tides. 17. What is 
the chief cause of ocean currents? 18. What other causes can you mention? 19. 
Describe the course of the equatorial currents in the northern and in the southern hemi- 
spheres. 20. Trace the Gulf Stream and the Japan Current. 21. What is the cause of 
counter-currents? 22. Write a paragraph on the effects of ocean currents. 



CHAPTER XV 

THE ATMOSPHERE 

Composition. Air is a mixture of gases. Oxygen and 
nitrogen are the most abundant, forming || of the whole. 
Carbon dioxide and water vapor are next in importance. 
Besides these, there are several other gases found in small 
amounts. Oxygen is the most important substance in 
nature. It composes -5" of the weight of the air, | of 
the weight of the water, and, by combining with other sub- 
stances, makes up fully ^ of the whole earth. It sup- 
ports both plant and animal life, and causes fire to burn. 
Dissolved in water, it supports the life of the ocean, though 
some animals like the whale come to the surface to breathe. 

Gently warm a tin cup of water and the dissolved particles of 
oxygen will be expanded and driven to the surface. They may be 
seen clinging to the bottom and sides of the vessel. 

Carbon Dioxide. When animals breathe or when fire 
burns, this gas is formed. Carbon dioxide supports plant 
life just as oxygen supports animal life. The plant retains 
the carbon and gives up the oxygen, while animals by 
respiration inhale oxygen and give out carbon dioxide. 
Nitrogen composes about % of the weight of the air, but is 
not important, its use being chiefly to dilute the oxygen. 
The amount of water vapor in the air at any given time 
varies according to place and temperature. 

Pressure and Weight. The atmosphere encompasses 
the earth on every side and penetrates into all cavities of 
the earth. We do not know how high above the earth it 

99 



lOO 



PHYSICAL GEOGRAPHY 



extends, but J/i of its weight is within ten miles. Its 
densest layers are next to the earth, and it grows thinner 
and lighter as the distance from the earth increases. It 



"""/lOO " 

— -7/a-- 
Tf 


Trso ~ 

-----k-- 


"'"ZAA '" 

ToTa 
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1 jj 


50 

BAROMEreH 

IN INCHES 


DEN SI TV OF 
AIR 


HEIGHT IN 
MILES 


SEA LEVEL 



Fig. 86. Chart showing the density of the atmosphere and the height of the 
barometer at different elevations. 



is known, however, to reach a height of several hundred 
miles, though human life cannot exist at a greater height 
than seven miles. 

The barometer is an instrument used to measure the pressure and 
weight of the atmosphere. A glass tube (Fig. 87) is closed at one end 
and filled with mercury. When the tube is placed upright, it is found 
that the mercury remains at a certain height in the tube. What keeps 



THE ATMOSPHERE 



it there? Clearly it must be the downward pressure of the air at the 
open end of the tube on the surface of the liquid at A. If the end of 
the tube were i square inch in area, the mercury column A B would 
weigh 14^ pounds. That is, a column of air i inch square at the base 
and extending upward as far as the atmosphere reaches, weighs 14^4 
pounds at the sea level. For convenience, the barometer tube is much 
smaller and the column of mercury is 30 inches high. When the barom- 
eter is carried into elevated regions, the mercury falls about one inch 
for 1,000 feet of ascent. It may thus be used to measure the height of 
mountains. Its other use is in connection with the weather (see 
page 128). 

The temperature of the air is measured by the ther- 
mometer. This is a closed tube with a 
bulb at one end, and contains mercury. 
The space above the mercury, as in the 
barometer, is a vacuum. Since the mercury 
expands when heated and contracts when 
cooled, temperature is measured by the rise 
and fall of the mercury column. There 
are several forms of the thermometer. One 
commonly used is Fahrenheit's, in which 
the boiling point of water is marked 212° 
and the freezing point 32°. In the Centi- 
grade thermometer, the boiling point is 
marked 100° and the freezing point, 0°. 

Forms of Moisture. The moisture in 
the air comes from the evaporation of 
water upon the earth or sea. This process 
goes on at all temperatures, so that the 
air always contains more or less moisture. 
The air and the moisture it contains act 
like a great blanket to keep the earth 
warm. Without them, the earth would 
soon lose its heat and would become too 
cold to support life of any kind. 



LJ^ 



Fig. 87. 
The Barometer. 



I02 



PHYSICAL GEOGRAPHY 



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-100 




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--80 






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.-60 






-50 






-40 






-30 






.-£0 






-10 






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Moisture in the Atmosphere. The air always contains 
a greater or less amount of moisture depending upon its 
temperature. Warm air is able to contain more than cool 
air, and evaporation continues until the atmosphere con- 
tains all it will hold. At this point it is said to be saturated. 
A cubic foot of air at 50° F. contains about four grains of 
water vapor. At 70° it contains eight grains. At 100° 
it will hold about twenty grains. 

^=^ The moisture of the air is usually in the form of invisible 

J[ )L vapor. During the day evaporation goes on rapidly; damp 
^ - ^^ surfaces are dried and water vapor from the ocean is taken 
up freely by the air. When air which is saturated is cooled, 
it gives up a part of its moisture in the form of rain, 
snow, etc. 

Humidity. We commonly speak of the moisture 

of the atmosphere as humidity. The actual 

amount of water vapor present in a unit volume 

of air is called its absolute humidity, and the ratio 

which the absolute humidity bears to the quantity 

of vapor which the same amount of air would 

contain if saturated is called relative humidity. 

Fill a tin vessel with ice and water. Stir the ice through 
the water until dew begins to form on the outer surface of 
the vessel. Then insert a thermometer into the mixture 
and after a minute or two read the temperature. This will 
be the same as the surface of the cup outside and of air 
which is in contact with the cup. The temperature at which 
moisture begins to condense out of the atmosphere is called 
the dew point. 

Forms of moisture. When the invisible vapor 
of the atmosphere is cooled it condenses slightly 
and becomes visible vapor. When this occurs at 
the surface of the earth, such vapor is called fog. 
Fig. 88. or mist, but when it takes place at some distance 
milliter" above the earth it is called cloud. Fogs and 



THE ATMOSPHERE 



mists are usually seen in 
the morning when the 
surface of the earth is 
cooled. But after the 
rising of the sun warms 
the earth they change 
to invisible vapor. As 
clouds and fogs are 
partially condensed va- 
por, they are heavier 
than the invisible vapor, 
and hence tend to settle 
down through the air 
toward the earth. 
When, however, they 
reach the warmer layers 
of the atmosphere they 
change into invisible 
vapor, and disappear. 

Varieties of Clouds. 
Clouds have several 
forms, which may be 
grouped into four 
classes. The high, 
feathery clouds, called 
cirrus, are composed of 
small ice crystals — so 
small that they are kept 
afloat at the height of 
several miles by the air 
currents. The clouds 
that we frequently see 




Fig. 89. Forms of clouds, i. Cirrus. 

tus. 3. Cumulus. 4. Nimbus. 



2. Stra- 



I04 PHYSICAL GEOGRAPHY 

along the horizon arranged in long lines are called 
stratus, or layer clouds. The heavy, dark masses of 
clouds which often precede a summer thunder-storm are 
called cumulus clouds. Clouds which are being condensed 
into rain or snow are called nimbus clouds. They may 
be seen as light gray ragged masses traveling rapidly before 
the wind that brings a shower. They are usually con- 
densed portions of cumulus clouds. 

Rain, Snow, and Hail. All clouds consist of water vapor 
in a partial state of condensation. When the particles of 
moisture become so heavy that the air can no longer support 
them, they fall in the form of rain, snow, or hail. If a 
partially condensed cloud passes into a layer of air below 
the freezing point, the little particles of moisture expand 
into crystals and fall as snow. The snow crystals take on 
many curious forms, but all of them are six pointed, thus 
having an angle of sixty degrees formed by two adjacent 
branches. (Fig. 90) 

When vapor condenses above the freezing point, rain 
is formed. When the condensing drops of vapor fall 
through layers of air below the freezing point, the result 
is hail. Hailstones are often built up of successive layers, 
evidently having fallen through alternate layers of vapor 
and cold air. They are sometimes an inch or more in 
diameter and resemble irregular masses of partially com- 
pacted ice. 

Dew and Frost. As we have seen, in the experiments 
above, when air comes in contact with any substance below 
the dew point the water vapor condenses out of it in the 
form of dew. If the condensation takes place in a tem- 
perature below the freezing point the vapor is deposited 
in the form of frost. 



THE ATMOSPHERE 



loS 



The common expression, "the dew falls," is incorrect, as dew forms 
by the condensation of moisture from the air which touches the objects 
where the dew appears. Neither is frost formed by the freezing of 
dew, but by the deposit of minute ice crystals on objects in contact 
with the air from which the crystals are precipitated. On clear nights 






■w -/ 



I ^"^ I.. - -^ . ; ( » 



:#^b -^-bt^ij ■ «^.- ^i0::i!§^' .^f ^ 



* . ■ "T 



f^ - ^T% -^"T^^ d^ 






j^. ^^:j^ I^' jpi 'I^ J^i 



' ^: \ l ->-%^^ 



^Jf^.^/Mk" 



Fig. 90. Forms of snow crystals. 

more dew will be deposited than on cloudy nights, because clouds 
prevent the radiation of heat from the earth and the objects on it. In 
the same manner any form of protection, as paper, cloth, a tree, or 
cover of any kind, will help to retain the heat and prevent the formation 
of dew or frost. Objects which radiate heat quickly, such as leaves, 
grass, metals, and stones, will have a heavier dew upon them than 
objects which retain their heat. Much of the dew is deposited from 
moisture which rises from the earth. Hence lowlands and swamps 
will have heavier dew than hilltops, because more moisture rises from 



io6 PHYSICAL GEOGRAPHY 

them and also because the air in the valleys is heavier and colder than 
the air on the higher ground. The cold air settles down into the low 
places and the warmer air rises to the higher places. Air movements 
prevent the formation of dew by carrying away the moisture as soon 
as it turns to vapor. A still, clear night is the most favorable for the 
formation of dew and frost. 

REVIEW. I. What are the chief gases composing the atmosphere? 2. How can 
you show that water contains oxygen.? 3. How is carbon dioxide formed and what 
becomes of it? 4. Why is the atmosphere densest at the surface of the earth? j. What 
is the height of the barometer at a distance from the surface? 6. What does this show 
about density? 7. Describe the construction of the barometer. 8. What are its chief 
uses? 9. Describe Fahrenheit's thermometer. 10. How is the centigrade thermometer 
constructed? 11. What would be the result if the earth had no atmosphere surrounding 
it? 12. How is climate affected by a lack of moisture in the air? Compare desert 
climates. 13. How are clouds formed? 14. Mention and describe four varieties of 
clouds. 15. Define fog, mist, dew, frost, hail, rain, and snow. 



CHAPTER XVI 

TEMPERATURE AND PRESSURE 

Heat Belts or Zones. The temperature of the earth 
and the atmosphere above it depends mainly upon the 
direction of the sun's rays. U it depended on this alone, 
these rays would divide the earth's surface into five heat 
belts or zones. When the sun is farthest north, its per- 
pendicular rays would trace the tropic of Cancer, its 
horizontal rays the Antarctic circle. When the sun is 
farthest south, its rays would in like manner trace the 
tropic of Capricorn and the Arctic circle. This would 
give one hot zone, two temperate, and two cold zones. 

Unequal Heating. The unequal heating of the earth is 
due to several causes besides latitude. The most impor- 
tant of these is the fact that land takes up heat quickly 
and loses it quickly, while water takes it up slowly and 
loses it slowly. The effect of this principle alone would 
be to make the land very hot in summer and very cold in 
winter, while the water would have a moderate temperature 
throughout the year. The movements of the water tend 
to counteract the effects of unequal heating. As we have 
seen (page 95), the cold waters of the ocean flow toward 
the equator and the warm waters toward the poles. The 
uneven surface of the land affects temperature in several 
ways. For every 300 feet of elevation, the temperature 
will be one degree Fahrenheit colder. Hence the moun- 
tain regions will be cooler than the lower plains. The 
direction of mountain ranges affects temperature. If 

107 



PHYSICAL GEOGRAPHY 



they extend east and west, they may shut off the cold 
winds from the polar regions and make parts of the land 
warmer. The central plain of North America owes its 
cold winter to the fact that the mountains run north and 
south, and thus allow the cold winds to sweep down from 
the north. 

Isotherms (equal heat lines) are lines which divide the 
earth into true temperature belts. They are drawn across 
the earth from east to west, connecting all places having 
the same average temperature for any given time. Thus 
we may have isotherms for the whole year or we may have 
winter and summer isotherms. If the temperature of a 
place is taken every day in the year at the same hour, and 
the sum of these records divided by 365, we shall have 
the average annual temperature of the place. 

Heat Belts Movable. A study of the isotherms for 
January and July will show that the heat belts or zones are 
not fixed, but that they move north in summer and south 
in winter, following the sun. The isotherm of 80°, which 
crosses the United States in July, is found at the equator 
in January, 40° of latitude farther south. If we compare 
the isotherms of the land with those of the ocean, we shall 
find that the shifting north and south is much less on the 
ocean. The rains and winds are, like temperature, partly 
dependent also on the direction of the sun's rays. Rain 
belts and wind belts therefore shift north and south, follow- 
ing the sun. 

Atmospheric Pressure, as before mentioned, is measured 
by the barometer. At the sea level the mercury column 
averages 30 inches; this is taken as the standard of pressure 
and is called "one atmosphere." The pressure of the 
atmosphere is due to its actual weight; and this varies 



TEMPERATURE AND PRESSURE 



TOO 




Fig. 91. The heat belts in July. 




Fig. 92. The heat belts in January. 



PHYSICAL GEOGRAPHY 



according to temperature and the amount of water vapor 
that the air contains. A rise of temperature and decrease 
of vapor make the air lighter. The temperature and 
pressure of the air are of great importance because they 
help us to understand and predict the force and direction 
of winds and storms, and the occurrence and amount of 
rain and snow. 

Isobars are lines connecting places on the earth having 
the same atmosphere pressure. They are named by 
giving the reading of the barometer at these places. 
The important use of isobars is to determine tht 
direction and velocity of the wind. Winds blow from 
high pressure to low pressure, as shown by the arrows that 
cross the isobars (page 129). The velocity of the wind will 
depend upon the variation in pressure, or gradient. 

REVIEW. On what does the temperature of the earth mainly depend? 2. Give 
the location of each of the five heat belts according to latitude. 3. What is the effect on 
climate of the ability of land and water to take up and retain heat.? How do the waters 
of the ocean help to distribute heat.'' 4. How does elevation affect temperature.'' 
5. Effect of mountain ranges and valleys on temperature. 6. What are isothermal 
lines? 7. Trace the isotherm of thirty degrees for January (Fig. 92) and account for its 
irregularity. Trace, also, the isotherm of sixty degrees for July. 8. Trace the thermal 
equator for each of these months, and compare its course with that of the geographical 
equator. 9. Compare the position of the heat belts in January with the corresponding 
heat belts in July. 10. What is meant by atmospheric pressure? 11. How is it meas- 
ured? 12. What are isobars? 13. How are they located and named? 14. How do isobars 
determine the direction of the wind? 15. What is meant by gradient? 



CHAPTER XVII 

WINDS, RAINS, AND STORMS 

Cause of Air Movements. The atmosphere Is kept in 
continuous motion through the unequal heating of the earth 
and the resulting inequalities of atmospheric temperature 
and pressure. Warm air is lighter than cool air; hence it 
rises, while the cool air flows in to take its place. If we 
open a door between a cold room and a warm room the cold 
air will flow along the floor into the warm room and the 
warm air will flow along the ceiling into the cold room. 
This process will continue until the air of both rooms is 
of uniform temperature. It is a matter of common ob- 
servation that the heated air near a lamp, a stove, or any 
other source of heat, is continually rising and that cool air 
is flowing in toward the source of heat. Thus the effect 
of unequal heating is to establish a circulation of air by 
which a uniformity of heat is established. 

The regions of the earth lying along the equator are 
intensely heated by the direct rays of the sun. In these 
places, therefore, the heated air is rising and flowing both 
north and south toward the colder regions of the temperate 
and frigid zones. From these cold regions, currents of 
cool and heavy air are flowing along the surface of the 
earth toward the equator to replace the rising and pole 
seeking currents. As the warm currents travel through 
the upper air to the poles, their temperature falls; and as 
the cold currents travel southward along the surface 
toward the equator, their temperature rises. It follows 



112 



PHYSICAL GEOGRAPHY 



that a point will be reached where the north seeking cur- 
rents will descend to the earth and where the currents 
traveling toward the equator will rise into the upper 
atmosphere. This place on the earth is in the neighbor- 
hood of 30° north and south of the equator. As the cur- 
rents of air are 
either rising or 
sinking at these 
places, they are 
regions of calms. 
At the equator, 
also, where the 
air currents are 
rising, there is a 
region of calms. 
The diagram 
(Fig. 93) shows 
the general cir- 
culation of the 
atmosphere if 
the earth had a 
uniform surface 




Fig. 93. Constant winds and calms. 



and no movement of rotation. Owing, however, to the 
diiferences between land and water and to the rotation of 
the earth, the actual circulation of the atmosphere deviates 
greatly from the system shown in the diagram. 

Effect of the Earth's Rotation. The velocity of the 
earth's rotation at the equator is, as we have seen, about 
1,000 miles an hour, and diminished to zero at the poles. 
Though the atmosphere is drawn toward the center of the 
earth by the force of gravitation, it is the lightest and 
most movable part of the earth's substance. Hence, 



WINDS, RAINS, AND STORAIS 



113 





while the earth rotates toward the east, the atmosphere, 
being less firmly held by attraction than the solid and 
liquid parts, has a motion in the opposite direction. This 
opposite motion would be greater in the regions of the 
earth having the greatest velocity of rotation. The 
movement of the air currents upon the earth is extremely 
compHcated and the causes are not fully understood. 
The westward currents set up along the equator by the 
earth's rotation turn 
northeastward in the 
northern hemisphere 
and southeastward in 
the southern hemi- 
sphere. Their effects 
die out in the regions 
of the tropics. Beyond 
the tropics the winds 
are uncertain and irreg- 
ular until the latitude of forty degrees is reached. At this 
point the winds blow steadily from the west with a tendency 
toward the polar regions. As they approach the poles 
they tend to whirl spirally about them in the direction of 
the hands of a clock in the south polar regions and in 
the opposite direction in the north polar regions. 

The effect of the rotation of the earth in deflecting air currents from 
the north and south direction may be illustrated by rotating a globe 
from west to east. While it is in motion draw lines along a meridian 
from the equator toward the poles. We shall have a series of curves 
which bend eastward, increasing their curvature as they approach the 
poles. In a similar manner if lines are drawn from the poles toward 
the equator they will curve toward the west. This teaches us that the 
pole seeking air currents are bent eastward and that those moved in 
the opposite direction are bent westward. 

Classes of Winds. The currents of air moving west- 



Fig. 94. Effect of rotation of the earth on the 
direction of air currents. The cut on the left shows 
the effect on currents moving from the equator 
toward the poles. The cut on the right shows the 
effect on currents moving from the poles toward 
the equator. 



114 PHYSICAL GEOGRAPHY 

ward and turning to the northeast and southeast are 
known as the trade-winds. Since they blow steadily 
throughout the year, they belong to the class called con- 
stant winds. To this class also belong the prevailing 
westerly winds of the temperate regions. Between the 
region of the trade-winds and that of the westerlies, the 
winds are uncertain and changeable. Hence these are 
regions of variable winds. The constant winds of the 
earth are sometimes known as planetary winds, because 
they belong to the planet as a whole. These wind belts 
shift north and south, following the sun as it moves 
back and forth between the solstices. Hence the areas 
of both constant and variable winds are continually 
changing. 

Periodic Winds are those which reverse their direction 
according to the change of seasons or as the result of 
unequal heating. Monsoons are periodic winds, caused by 
the shifting of the heat belts of the earth. The monsoons 
of the Indian ocean are the most noted (Fig. 95). During 
the northern summer the equatorial heat belt shifts north 
of the equator and the southeast trade-winds bend east- 
ward, becoming the southwest monsoons. During the 
northern winter, when the heat belt shifts south of the 
equator, the northeast trades bend eastward, becoming 
the northwest monsoons. This variation in the direction 
of the winds is partly caused by the rotation of the earth 
and partly by the intense heating of land masses, by which 
the winds are drawn toward the heated regions. As the 
monsoons sweep across the Indian ocean they carry with 
them vast masses of vapor which condense to rain in 
traversing the land. The direction of all classes of winds 
is affected by the direction of river valleys and mountain 



WINDS, RAINS, AND STORMS 115 

ranges. The winds tend to blow parallel with the valleys 
and with the ranges, following the paths of least resistance. 

Land and sea breezes are periodic winds caused by un- 
equal heating of land and water along the coast. As 
the land is heated more rapidly than the water, the cur- 
rents of air are drawn toward the land during the day, 
forming a sea breeze. At night the land cools rapidly 
while the water retains its heat. The result is a land 
breeze. Sailing vessels take advantage of the land breeze 
by leaving port before daybreak. 

Rainfall. The general theory of rainfall and its dis- 
tribution has already been discussed. The vapor rising 
from the ocean is blown landward with the wind, and is 
condensed by meeting the cold air of elevated regions or 
by being carried into the upper and colder layers of the 
atmosphere. The amount of evaporation depends upon the 
intensity of the sun's rays and upon the movement of air 
over the surface of the ocean. The capacity of the air 
to retain vapor depends also upon its temperature. The 
following general laws may be laid down in regard to 
rainfall: i. Rainfall is greatest at the equator and dimin- 
ishes toward the poles. 2. The rainfall on the coasts of 
the continents and on the windward sides of cool slopes 
and mountains is greater than on interior plains. 3. In 
the region of the trade-winds, the greater rainfall occurs 
on the eastern slopes and coasts of the continents. In 
the region of the westerly winds the rainfall is greatest on 
the western slopes. 

The Tropical Rain Belt. A study of the rain chart 
(Fig. 95) shows that the region of heaviest rainfall lies 
along the equator. The trade-winds blowing from the 
northeast and southeast bring vast quantities of vapor 



WINDS, RAINS, AND STORMS 117 

into this region and the rising currents of air carry it to a 
sufficient height for condensation. In many parts of the 
tropical regions, rains occur daily. A study of the charts 
(Figs. 91 and 92) shows that the region of tropical rains 
shifts northward during our summer and southward dur- 
ing our winter, which is the summer of the southern hem- 
isphere. This regular movement of the rain-belt produces 
the wet and dry seasons of the tropics. It will be noticed 
that the region of calms bordering the equator is traversed 
twice a year by the rain belt, and hence will have two wet 
seasons and two dry seasons annually. In the regions 
beyond the equatorial belt of calms the wet season comes 
in summer and the dry season in winter. 

Desert Belts. When winds pass over elevated regions, 
the moisture is largely condensed from them by the cool 
atmosphere. When after passing such regions, the winds 
descend again to lower plains, they become warm and able 
to take up more moisture. Thus they become drying 
winds, and the land over which they pass is usually barren. 
It is in this way that the Sahara and most other deserts of 
the world are caused. Such regions are barren not be- 
cause the soil is unfertile but because of the lack of mois- 
ture. The so-called desert regions of the United States 
have proved, when irrigated, to be wonderfully productive. 
Occasionally deserts are crossed by low mountain ranges 
which arrest enough moisture to fertilize the soil and to 
feed streams of considerable size. Such streams flow 
during rainy weather, but for the rest of the time they 
are dry gorges and are frequently used as roads. 

Rainfall Beyond the Tropical Belt. The rainfall in the 
temperate regions of the earth is subject to great varia- 
tions due to local causes. The western coast of North 



ii8 PHYSICAL GEOGRAPHY 

America and the greater part of the continent of Europe 
are watered regularly by rains brought by the prevailing 
westerly winds. The interior regions of North America 
are dependent upon the northern limit reached by the 
tropical rain belt and upon the eastern limit reached by the 
westerly winds. As these limits are variable, so the regions 
dependent upon them for moisture occasionally suffer 
from drouth. The eastern part of North America, having 
no mountains to interrupt the force of the winds, has a 
rainfall varying from 60 inches at the gulf of Mexico 
to 30 inches at Hudson Bay. The source of the rain is 
mainly the great cyclonic whirls which originate in the 
tropics. The regions of Europe and of Asia lying far from 
the coast or hemmed in by mountain ranges are neces- 
sarily dry. 

The rainfall of any region is measured in inches per 
year. When it reaches 40 inches and is well distributed 
throughout the year, agriculture may be profitably carried 
on. A rainfall of less than 10 inches is insufficient for 
growing crops except by special methods or by the aid 
of irrigation. The heaviest recorded rainfall in the world 
is that in the region north of the bay of Bengal, where it 
has been known to reach 600 inches annually. The 
lowest record is that of the Mohave desert, in California, 
where less than 2 inches annually has fallen. 

Storms. When the velocity of the wind increases to 
a mile or more per minute, it becomes a storm, rain or 
snow, and sometimes thunder and lightning accompany- 
ing it. A storm is usually the result of a disturbance of 
the atmosphere in some particular locality, but when 
once started it takes a direction fixed by the usual course 
of the winds in that place. Cyclones are whirling storms. 



WINDS, RAINS, AND STORMS 



IIQ 



The whirl may be of all sizes, from the little dust whirl- 
wind at the street corner to a storm that covers half a 
continent. To understand the beginning of a cyclone, let 
us suppose that in a certain locality the barometer is 
"low." This means that the air is light and rising. A 
low area usually has ' ' high " 
areas surrounding it, per- 
haps at a distance of hun- 
dreds of miles. In "high" 
areas the air is heavy. The 
heavy air from the high 
areas soon begins to flow 
toward the low area. The 
air currents take on a spiral 
motion which grows swifter 
and swifter as they approach 
the center. 

The movement of water flow- 
ing out at the bottom of a circular 
wash basin illustrates the forma- 
tion of a spiral. 

The dry air flowing out- Fig. 96. The anemometer, an instrument 

ward from the region of high ^°' "^^^«^"^g ^he velocity of the wind. 
pressure also moves in a spiral and is called the anticyclone. 
In the northern hemisphere the direction of the whirl is 
opposite to the movement of the hands of a clock, but this 
direction is reversed in the southern hemisphere. The 
air above the low area is warm and damp. When it rises 
into the cooler air above it the vapor is condensed, and 
rain follows. The rain will be heaviest at the storm 
center, as the center of the whirl is called. A very violent 
rainfall at the storm center is cometimes called a cloud- 




I20 PHYSICAL GEOGRAPHY 

burst. It is caused by the rapidly rising air currents, 

which hold the water suspended for a time, but afterward 

it comes down in sheets and continuous streams. Cyclonic 

^^ .»^ 4^ — ^*---.>t Storms have an 

"^ ^ /V >«<' "^-v^ ^ onward motion, 

/ // /IIn ^ \ \W ( f^-^ ^ crossing the iso- 

* V \\\ \' \\'a bars into regions 

}v^"";M U ^ V^W/// of low barom- 

V_^^7 //) \\V^'^/ eter. In the 

^^^/M ^ ^^_j^/ United States 

thev cross the 

Fig. 97. The movement of air currents from high to low ^ 

pressure areas. COUntry frOm 

west to east, or from southwest to northeast, following the 
Atlantic coast. In the northwest, these storms are some- 
times accompanied by fine, hard snow crystals, which cut 
like knives when driven by a high wind. Such a storm is 
called a blizzard. 

The weather maps on page 129 show the path of a low area from 
the northwest across the United States. Notice that the arrows 
showing the direction of the wind, cross the isobars at right angles, 
or nearly so, and move spirally about the low area. Fig. 96. Anticyclones 
follow the path of the cyclones. They bring clear weather, and take 
the name of cold or cool waves when they come from the northwest, and 
warm or hot waves when they come from the southwest. 

A Tornado is a violent cyclone of small diameter. It 
is caused by a layer of warm, moist air breaking through 
an overlying stratum of cold air. The moist air rushes 
through the opening, taking the form of a huge, dark 
funnel which hangs from the clouds, small end downward. 
The rapid rise of the moist air causes the surrounding 
heavy air to rush into the path of the tornado with destruc- 
tive violence. Everyone has noticed the rush of air into 
the wake of a swiftly moving train. It resembles some- 



WINDS, RAINS, AND STORMS 



121 



what the rush of air toward the tornado funnel, only while 
the train may be moving at the rate of 50 miles per hour, 
the velocity of the tornado is often six times as great. A 
tornado at sea draws up a column of water into its funnel, 
and is called a waterspout. 




Fig. 98. A tornado on the great plains of the West. 

Typhoon and Hurricane are names given to violent 
tropical cyclones in the Indian and Atlantic oceans, respec- 
tively. They are more severe than storms on land, as there 
are no irregularities of surface to check their course. When 
the West Indian hurricanes strike the coast a violent 
wave sometimes accompanies them. It was such a hur- 
ricane and wave that destroyed the city of Galveston 
in 1900. South of the equator these storms move south- 
east instead of northeast, as in the northern hemisphere. 

Storm Charts. Sea captains avoid the storm center by taking a 



PHYSICAL GEOGRAPHY 



course which carries them out of its path. By a study of the storm 
charts it appears that if you stand facing the wind, the storm center 

is on the right north of the 
equator, and on the left 
south of the equator. The 
ship, to escape the storm, 
must therefore sail with the 
wind on the right in the 
northern hemisphere and on 
the left in the southern. 

Thunder-storms. 

The most awful thun- 
der and lightning 
usually accompany 
tornadoes and tropical 
cyclones. But local 
thunder-storms are fre- 
quent toward the close 
Fig. 99. A Waterspout. of hot, humid days in 

summer. The vapor expanded by the hot earth rises to 
the height of a mile or more and gathers in great cumulus 




NOPITHER.N HEMISPHERE 



SOUTHERN HEMISPHERE 




Fig. 100. Storm cards for the northern and southern hemispheres. To escape the 
storm center, the ship takes a course so that the wind blows from right to left in the 
nothern hemisphere and from left to right in the southern hemisphere. 



WINDS, RAINS, AND STORMS 



123 



clouds. After a time these condense Into rain. The rapid 

condensation and the friction of moving masses of vapor 

cause electricity, or 

lightning, to flash from 

cloud to cloud, or from 

the clouds to the earth. 

As the center of the 

storm approaches, a 

column of .cold air 

descends with the rain 

and spreads out at the 

bottom. 




Fig. lOi. Diagram showing the refraction of 
light by raindrops causing the rainbow. 



The Rainbow. A thunderstorm passing eastward in the late after- 
noon is usually accompanied by a "rainbow." The raindrops falling 
from the rear of the eastward moving clouds catch the rays of the sun 
and turn, or refract, them backward. As each color has its own angle 
of refraction, it is seen in a different position from the other rays as 
shown in Fig. 10 1. 

REVIEW. I. What is the chief cause of atmospheric movements.'' 2. Give illus- 
trations. 3. Describe the general circulation of the atmosphere upon the earth without 
regard to its rotation or the irregularity of its surface. 4. How is this system affected by 
the earth's rotation.'' 5. Name the three classes of winds. 6. How are the trade-winds 
caused? Where is the region of variable winds.'' 7. Describe the monsoons. 8. Land 
and sea breezes. 9. What is the cause of rainfall.'' 10. State the three principles govern- 
ing it. Describe the tropical rain belt and its movements. Desert belts. 11. What is 
said of the rainfall of the temperate zone? 12. How is rainfall measured.'' 13. What 
is a storm .^ 14. What are cyclones.'' 15. What is said of their size.'' 16. Anticyclones. 
17. Describe the rainfall during a cyclone. 18. What is a blizzard.'' 19. A tornadoi* 
20. Typhoons and hurricanes. 21. Storm charts. 22. Describe a thunder-storm. 23. 
Give cause of rainbow. 



CHAPTER XVIII 

WEATHER AND CLIMATE 

Difference between Weather and Climate. The pres- 
sure and temperature of the atmosphere with the resulting 
winds, rains, storms, and clouds are the elements that 
make both weather and climate. But weather is the state 
of the atmosphere with respect to these things at any 
given time, while climate is the average weather for a 
number of years. It is possible to have rainy weather 
in a dry climate or cold weather in a warm climate. 
We have cold winters and warm winters, wet seasons 
and dry seasons, in the same locality; but we find that 
the climate through long periods of time averages about 
the same. 

Varieties of Climate. If the average annual tem- 
perature of a given locality is 60°, we call the climate 
temperate. If the annual range of temperature is high, 
say from 90° in summer to 0° in winter, the climate is 
called extreme, or continental. But if the range is low, 
we call it an equable or moderate climate. A tropical 
climate is marked by an average temperature of 70° to 
80° with little variation in range. A dry climate with a 
moderate temperature is healthful; but a persistently hot 
and moist climate, or one subject to sudden changes, is 
unhealthful. There are so many elements determining 
climate that the climatic belts of the earth vary greatly 
from the zones and from the rain, wind, temperature and 
pressure belts. As none of the elements of climate con- 

124 



WEATHER AND CLIMATE 



125 



form with latitude, the cHmate of every well-defined 
natural division of the earth must be studied by itself in 
order to be understood. 

Elevation is an important cause of the Irregularities of 
climatic belts, since it aifects both temperature and rainfall. 
The plateaus among the middle Andes mountains have 




SCALE 
I I Less tliaii 20 inches 
|=::=t 20— iO inches 
^M 40-60 " 
^aa Over 60 " 



Fig. 102. Chart showing the average rainfall in the United States. 

a temperate and healthful climate with moderate rainfall, 
while the lowlands of Brazil in the same latitude are hot, 
moist and often too unhealthful for human habitation. 
The drying effect of mountains upon the winds that pass 
over them has been mentioned (page 117). In some of the 
Swiss valleys and on the plains bordering the eastern 
slopes of the Rocky mountains, these winds, called 
"foehns" and ''chinooks," evaporate even the snow and 
take the last drop of moisture from the soil. Dried by 



126 PHYSICAL GEOGRAPHY 



passing the mountains and warmed by descending into 
the valleys, these winds are thus able to take up a large 
amount of moisture. 

A uniform climate is most nearly approached in certain 
parts of the trade-wind belt and on coasts where winds 
are mainly from the ocean. Islands in the tropic seas 
like the Bermudas and the West Indies have an equable 
climate and a uniform rainfall. The western coasts of 
Europe and North America are in the region of westerly 
winds that are warmed by passing over ocean currents. 
The annual range of temperature is less than 20° and the 
air is uniformly damp and clou'dy in winter and dry and 
clear in summer. 

Climate and Weather in the United States. There are 
three broad climatic divisions in the United States. The 
Rocky mountains region has abundant rain in the north, 
where it is crossed by the westerly winds, but the southern 
half is almost a desert. The seasons are marked by 
extremes of heat and cold. This region is a good example 
of a continental climate. The lowland plains and the 
eastern coast of the United States, as shown on the map, 
are in the path of the cyclones and anticlones that traverse 
the country from west to east, and occasionally coming 
from the east and south. Cold, dry, and agreeable weather 
usually comes with the west winds in summer. This 
may continue for several days. Then the air becomes 
moist and warm; a thunder-storm breaks over the coun- 
try, followed again by clearing and pleasant weather. 
In the spring, and especially in late summer and autumn, 
tropical storms of longer continuance sweep up the coast, 
bringing several days of rainy weather at a time. Dur- 
ing the winter the storms are usually from the north 



WEATHER AND CLIMATE 



127 



and east, while those from the south come very seldom, 
and when they do come bring rain and thaws. 

Weather Forecasts. Careful observation for a series of 
years shows that the weather of any locality is repeated 
with slight variations year after year. About fifty years 




Fig. 103. Chart showing the usual path of storms in the United States. The heavy 
lines show the direction of storms, and the dash lines crossing them show the average 
daily progress of a storm center across the country, from west to east. 

ago the signal service of the army began to record obser- 
vations in regard to temperature, winds, and storms. 
Later the Weather Bureau was organized and signal 
stations were established in various parts of the coun- 
try. At present there are about 85 of these stations, 
located in regions where weather phenomena can be best 
observed. A large number are along the Atlantic and 
Gulf coasts; some are in the valleys of the Ohio the 
Missouri, and the Mississippi rivers; about 25 are in the 



128 PHYSICAL GEOGRAPHY 

mountain regions and on the Pacific coast; and others are 

along the Great Lakes. 

Each morning at 8 o'clock, observations are made and telegraphed 
throughout the country. These observations include the barometer 
reading, temperature, direction and velocity of the wind, rainfall and 
the appearance of the sky. Having this information, the "forecast" 
officials can predict the weather for the next 24 to 30 hours. Storm 
signals are then displayed along the coast to warn mariners what 
storms or winds are coming and weather maps are made and may be 
sent to fruit-growers, farmers, and to all those whose business is in any 
way dependent on the weather. 

Making a Weather Map. A map of the United States 
is printed, containing state boundaries, mountains, rivers, 
and plains, and the location of the signal stations. Each 
station is indicated by a circle. Through this an arrow 
is drawn representing the direction of the wind. If the 
circle is half blackened, the meaning is "partly cloudy"; 
if entirely blackened, "cloudy." Next, the temperature 
of each station is written, and isotherms are drawn con- 
necting all stations having the same temperature. The 
pressure readings are next put in and examined to see 
which is the lowest. The station having this will be the 
center of the low-pressure area. This area is enclosed in 
a circle and the isobars are drawn. 

The direction of the wind will be found to be nearly 
vertically across the isobars from high to low pressure. 
The succession of readings from high to low pressure is 
called gradient. The more the readings vary, the 
"steeper" the gradient and hence, the greater the velocity 
of the wind. The winds travel in a spiral movement 
toward the low centers and away from the high ones. 
The former are called "cyclones" and the latter "anti- 
cyclones." Cloud vapor is continually being forced by 
the cyclonic whirls into regions of low pressure, where. 




300 «. 2,^75- U- S. Departmem of Agriculture. 
30^ ®„a«=^r WEATHER BUREAU 




EXPLANATORY NOTES. 
Observations taken at 8 a.m,, 75th meridian 
pressure reduced to sea level. 

IsotiafS, continuous lines, pass through points of equal 
pressure. 

Isotherms, dotted lines, pass through points oS equal tem- 
peiature; drawn only for zero, freezing, 90, and 100 degrees. 
O Clean 9 Partly Cloudy; # aoudy; R Rain; S Snow; 
M Report missing. Arrows nj with (he wind. 
First figures indicate temperature; second, precipitation of 
.01 inch or mon;. 



Fig. 104. Weather maps on two successive days in February, 1912. Notice the 
movement of the high and low pressure centers during twenty-four hours, 

129 



I30 PHYSICAL GEOGRAPHY 

rising into the upper and cooler regions of the atmosphere, 
it is condensed to rain or snow. 

REVIEW. I. What are the elements of weather and climate? 2. How does climate 
differ from weather? 3. Name and describe some of the varieties of climate. 4. What 
is the effect of elevation on climate? 5. Give reasons why climate does not exactly 
correspond with latitude. 6. What is said of the drying effects of winds? 7. In what 
parts of the world is the climate most uniform? 8. Describe the climate of the Rocky 
mountain region of the United States. Of the region of central lowlands. 9. Describe 
the climate of the eastern coast of the United States. 10. Describe the work of the 
Weather Bureau. 11. How is a weather map made? 12. Meaning of symbols used. 



CHAPTER XIX 

PLANT LIFE 

Organic and Inorganic Nature. The air, the sea, the 
soil, and the rocks belong to the inorganic kingdom. This 
means that in these things there is no distinction of parts. 
A rock may be broken in pieces and each is still a rock. 
But plants and animals belong to the organic kingdom. 
They are made up of various parts, or organs, each of 
which has a function; that is, something to do with the 
view to maintaining life and perpetuating its species. 
The root, the stem, and the leaf has each its own part in 
the growth of the plant, just as the heart, the lungs, and 
the stomach have their several functions in the life and 
growth of the animal. 

Relation of Plant and Animal. One of these relations 
has been mentioned (page 99), but plants and animals 
are dependent upon each other in several other ways. 
Most animals depend directly upon plant life for food, 
though some wild animals, as the lion, the tiger, the wolf, 
and the fox, are strictly carnivorous (flesh-eating) animals. 
Again, animals die and their bodies mingle with the soil, 
thus furnishing valuable nutriment for plants. The ero- 
sion of Hmestone rock, which is made chiefly of animal 
remains, furnishes a rich soil. Plants depend upon the 
heat and light of the sun, moisture, the air, and the soil. 
The most important of these is heat. No matter how 
favorable other conditions may be, unless there is the 
proper temperature for a sufflicient length of time, the 

131 



132 



PHYSICAL GEOGRAPHY 



plant will not grow and ripen. If the temperature is 
below 32°, the freezing point of water, the roots cannot 
take moisture from the soil, the sap chills and does not 
circulate, and the plant dies. For this reason, the tops 







Fig. 105. A tropical forest in the East Indies. 

of mountains and the extreme polar regions are nearly 
destitute of plant life. 

Zones of Plant Life. Each plant has a range of tem- 
perature in which it flourishes best. We may therefore 
divide the earth into plant zones according to temperature. 
Each of these zones has its characteristic forms of vegeta- 
tion. These forms are not the same in all of the con- 
tinents, owing to certain laws that govern the spread of 
plant life; but in size, luxuriance, and in number of species 
there is a regular gradation from the equator to the poles. 

Soil and water are necessary to plant life. The leaves 



PLANT LIFE 



133 



absorb water, which keeps them fresh and straight. 
But it is in the soil that water is most essential. Here 
it dissolves minerals that are the proper food of the plant, 
and the rootlets absorb this moisture and carry it upward 
to nourish the plant, 
just as the blood circu- 
lates in the body of an 
animal and nourishes 
the several parts. As 
the blood of different 
species of animals 
varies, so each plant 
has its own peculiar 
sap. Besides furnish- 
ing mineral food for 
the plant, the soil gives 
to the roots a firm 
anchorage maintaining 
the stalk, or trunk, in 
an upright position. 

Light and Air. The 
air brings to the plant 
carbon dioxide (page 
99), and the sunlight 
enables the leaves to absorb it and change it into sugar, 
cellulose, and other products which are peculiar to the 
plant. On the under side of every green leaf are very 
minute openings called stomata (mouths), through which 
the leaf breathes in the carbon dioxide. Each leaf con- 
tains a green material called chlorophyl (leaf-green), which 
has the power to break up the carbon dioxide into carbon 
and oxygen. The oxygen is given out again into the air, 




Fig. 106. An avenue of live oalis with Spanish 
moss in the southern states. 



134 



PHYSICAL GEOGRAPHY 



but the carbon combines with water to form the several 

organic compounds named above. Without sunHght there 

would be no chlorophyl cells, and hence no plant growth. 

Thus the leaves are not only the lungs which breathe in 

the carbon dioxide, but they are chemical laboratories which 

manufacture from it 

the products which 

belong to the plant. 

These products are as 
numerous as plants them- 
selves, and are important 
to mankind as drugs, dyes, 
medicines, beverages, foods, 
and raw materials. Every 
part of the plant furnishes 
something useful. The 
root, the trunk, the sap, the 
seeds, the fruit, the buds, 
the leaves, the pith, and 
the seed-wings all make 
some contribution to the 
comfort, health, and con- 
venience of man. 

The Equatorial Belt 

is the region of the 
greatest variety and 
growth of plant life. Heat, light, and moisture are there 
in abundance throughout the year. Growth goes on without 
check by the cold of winter or the drought of summer. 
Trees of great height and of countless kinds abound in the 
forests. Dense undergrowth, trailing vines, and air-plants 
spring up among them, and, clinging to the trunks and 
branches, form a thick jungle below and an interlacing 
canopy above, which make an intricate tangle, dark and 
almost impassable. Palms in many and useful varieties, 
hard cabinet woods, and fruits and spices are abundant. 




Fig. 107. A "buttressed" tree. 



PLANT LIFE 



135 



The Tropical Belts, with their hot summers and mild 
winters, lie next to the equatorial belt. Figs, dates, grapes, 
almonds, oranges, and lemons are characteristic fruits. 
Cotton, corn, rice, and sugar are the most valuable 
products. Pine, 
palmetto, cypress, 
and magnolia trees 
are the leading 
kinds. The red- 
wood, the baobob, 
the eucalyptus, and 
the banyan trees 
are the largest. 

The Temperate 
Belt is the home of 
deciduous trees, 
grains, and hardy 
fruits like the 
pear, apple, peach, 
cherry, plum, and 
quince. The oak, 
chestnut, ash, elm, 
maple, birch, beech, 
hickory, and numer- 
ous other species of 
trees are found. Plants known as herbaceous perennials 
are characteristic of this zone. The stalk and leaves of 
these plants die when the frost comes, but the roots live 
through the winter and send up a fresh growth in the 
spring. Others called annuals die altogether, and seeds 
must be sown every year to produce them. Numerous 
evergreens, as the cone-bearing trees, flourish in the cooler 




Fig. 108. An avenue of royal palms. 



136 



PHYSICAL GEOGRAPHY 



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In 




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Fig. 109. Gathering turpentine in a hard pine forest in the Southern states. 

parts of this belt, especially in the uplands and mountain 
regions. The mountain tops afford only the lower forms of 
plant life. If we should ascend a mountain in Mexico or 
South America, we might find the same succession of plants 
that one might find in a journey from the equator to the poles. 
The Cold Belt is the least productive of plant life. The 
long, cold winters and the deeply frozen ground kill all 

but the hard- 
iest varieties. 
Pines, spruce, 
birches, and wil- 
lows are found 
in the warmer 
parts of this 
belt, but there 
comes a limit, 
just as in ascend- 
ing a mountain, 
beyond w^hich no 

Fig. no. Palms along the Atlantic coast of Florida. 




PLANT LIFE 



137 



trees are found. Only mosses and lichens are found 
clinging to the rocks, and some water plants and mosses 
withstand the cold in the frozen swamps. In the short, 
hot summer of these arctic regions, hardy flowering plants, 
whose seeds have sur- 
vived the cold, spring 
up and make the slopes 
and tundras bright 
with patches of green 
and bits of color. 
Flowering grasses, 
saxifrages and poppies 
are among them. 

Air, Water, and 
Desert Plants. Plants 
are found that are 
adapted to varied sur- 
roundings. Some, like 
the orchis family, are 
air plants. They fasten 
themselves to some 
support and their roots 
take nourishment from 
the air. Some are 
parasites, living upon other plants. The dodder and the 
mistletoe are of this sort. They take root upon the oak, 
willow, and other trees and take up the sap for their 
own support. Many weeds that live in the sea may 
be found washed ashore on any beach. Many kinds of 
lilies, rushes, reeds, and mosses grow in swamps, and in 
shallow lakes and ponds. Rice grows in marshes along 
the shore; the willow, cypress, and the mangrove live in 




Fig. III. Gathering rubber in the forests along 
the Amazon river. 



1.^8 



PHYSICAL GEOGRAPHY 



swamps. The victoria regia is a noted water plant of the 
Amazon. It has flat leaves with upturned edges, often 
several feet in diameter. Some plants are adapted to a 
very dry soil. The sagebrush and the cactus of the South- 
west are such plants. They send roots deep into the soil, 
sometimes from 15 to 20 feet, in search of moisture. 




Fig. 112. Irrigated farms in Salt river valley, Arizona. 

The Spread of Plants. Nature provides in various 
ways for the spread of plant life. Some seeds are winged, 
or covered with down or hairs and are transported by the 
wind. The thistle, dandelion, and maple are familiar. 
Other seeds are contained in elastic pods, which fly open, 
throwing the seed to a considerable distance. Beggar's 
lice, burdocks, and "stick-tights" cling to men and animals. 
Birds, rivers, and ocean currents carry them to new fields 
and strange shores. The vegetation of oceanic islands is 
due largely to the movement of ocean waters. Besides 
these agencies, civilized men have carried useful plants, 



PLANT LIFE 139 



trees, flowers, fruits, and grains into every quarter of the 
habitable earth. 

Broad oceans, mountains, deserts, dense forests, and currents flowing 
between and not toward shores may prevent the spread of plants. 
In such cases the flora (plant life) of two continents may be utterly 
different. The flora of Australia is unlike that of any other continent, 
and that of South America is different from that of North America and 
Europe. 

Scientific methods of farming and gardening work great changes 
in the nature and value of plants. Cultivated fruits have little 
resemblance to their wild originals. One would hardly think that 
the jaqueminot and damask roses are descended from the humble wild 
rose that grows along the stone walls and in the neglected corners of 
the fields. 

REVIEW. I. Difference between organic and inorganic nature. 2. What is naeant 
by an organ? 3. Describe the relation of plants and animals in regard to food. 4. Effect 
of temperature on vegetable growth. 5. Relation of soil and water to plant life. 6. Show 
how plants are dependent on light and air. 7. Describe the plants of the equatorial belt. 
8. Plants of the tropical belts. 9. Plants of the temperate belts. 10. Plants of the cold 
belts. II. Describe plants which are adapted to a dry climate. 12. Name plants 
adapted to a wet climate. 13. What are air plants and parasites.? 14. How does nature 
provide for the spread of plants? 15. What are the chief barriers to the spread of plants? 
16. How are plants affected by cultivation? 



CHAPTER XX 



ANIMAL LIFE 



Animals and Plants Compared. Animals differ from 
plants in two important particulars. They have the 
power of moving from place to place, and are more in- 
dependent of climate, since their bodies have the power 
of maintaining a certain temperature. They are unlike 
plants again in that they can do without sunlight and 
that their food is mainly vegetable or animal. But, like 
plants, they must have air and water. 

Animals are adapted to their surroundings; their homes 




Fig, 113. Two-horned rhinoceros found in Africa. 
140 



ANIMAL LIFE 



141 



are made near the places that supply them with food. 
The robin builds in the cherry tree; the crane and the stork 
live near ponds; and the tiger makes his home in the jungle, 
where he can _ 

stealthily 
pounce upon his 
prey. If by any 
means the 
proper food of 
an animal is 
destroyed it 
must find a new 
home or perish. 
Every animal is 
fitted by nature 
for securing its 
food, for defense 
against its ene- 
mies, and for 
preserving its 

young. The Fig- iH- The reindeer. 

velvet feet of the cat and its sharp claws enable it to creep 
noiselessly upon its prey and to seize it. Unless the deer 
and the antelope were swift of foot they would soon be 
destroyed by their flesh-eating enemies. Every animal has 
its enemies, and life is a constant struggle for existence. 
The mole and rabbit burrow in the ground to escape their 
enemies, the weasel and the fox. But the weasel must 
himself avoid the fox, and the fox is in constant fear of 
the hounds. Birds build their nests in lofty trees to keep 
their eggs safe, or bury them in the earth or sand. Frogs 
lay their eggs in water, where the young tadpole may find 




142 



PHYSICAL GEOGRAPHY 



food; fish swim up the rivers and brooks and spawn upon 
the still, shallow places, where the eggs may be safe from 
swift water and the dash of waves. 

Succession of Animal Life. The species of animals 
now living have not always been upon earth, nor are all 




Fig. 115. The Springbok of Africa. 

of them likely to remain. Countless forms of animal 
life are found imbedded in the rocky layers of the earth's 
crust, or buried in swamps beneath the ice of the Arctic 
regions. Bodies of a species of hairy elephant and rhinoc- 
eros have been dug up in Siberia. In the western part 
of Europe, huge species of elephants, deer, oxen, horses, 
bears, lions, tigers, and hyenas are found, all of which 



ANIMAL LIFE 



143 




Opossum. 



are now extinct. In the United States are found the 
remains of huge lizards 20 to 30 feet in length, of birds 
with teeth, of the gigantic mastodon that stands 12 feet 
high, and of a thousand 
kinds of shellfish, in- v. MSfT^^^:*^^- 
sects, and lower forms 
of life. In recent times, 
the dodo and the duck- 
bill of the Australian 
region have become 
extinct, and the Amer- 
ican bison is nearly so. 
Only strict laws have 
preserved the ele- 
phant, deer, moose, and 
many kinds of birds and fish that are sought by sportsmen. 

Survival of the Fittest. Our present animals are only a few left 
out of the countless thousands that have lived upon the earth. By 
reason of their cunning, swiftness, strength, or ability to change their 
homes, they have survived the many changes in the climate and surface 

of the earth, and 

^^m^i^^^Mi^i^ ^^^ attack of ene- 
r ft».....i^vt^^f\\%^^^^^^^&^^»ffi^^M#»S),, mies. Animals with 

cumbersome bodies 
and without means 
of defense must give 
way to those of 
greater agility and 
fierceness. 

Distribution 
of Animals. 

Rivers, oceans, 
deserts, moun- 
tains, and for- 
Fig. 117. Wolf. ests are barriers 




144 



PHYSICAL GEOGRAPHY 




to the spread of animals, as they are of plants. Animals 
that can swim or fly can pass some of these boundaries. 
The swift sea-birds, the gulls, the pelicans, and petrels, 
pigeons, hawks, swallows, and cranes are found in every 

land. But in most 
cases, widely separated 
lands have different 
forms of animal life. 
The topography of the 
country, that is, its 
surface and elevation, 
somtimes explains the 
spread of animals, or 
their confinement to 
Fig. ii8. Marten. somc particular region. 

The chamois, sheep, wild goats, and the South American 
llama and alpaca are fitted only for mountain life, and could 
not live elsewhere. The hippopotamus and the alligator live 
on the banks of rivers for the same reason that the reindeer 
and polar bear live in the Arctic regions, because their 
bodies are adapted to such surroundings. Each animal is 
limited to a certain habitat, or range, as well as by natural 
barriers. Its habitat is the area within which it may 
find not only food and safety, but which is also best adapted 
to its habits of life. The domestic animals have been 
carried by men into every land. The horse, the cow, the 
sheep, pig, goat, dog, and cat seem to flourish in as great 
a variety of climate as man himself, if only food and 
shelter are provided for them. The animals that are 
not cared for in this way are confined to narrower bounds. 
The Realms and Regions of Animal Life. We may 
divide the earth into three temperature zones of animal 



ANIMAL LIFE 



145 



life, the Arctic, the Temperate and the Tropical. The 
Arctic realm abounds in birds, fur-bearing animals, deer, 
sea-animals, and fish. The polar-bear, seal, and walrus 
live upon the ice. The caribou, the musk ox, and reindeer 
live on the Arctic plains and feed on the scanty vegetation 




Fig. 119. Kangaroo. 

which they afford. Some of these animals are migratory 
and seek homes farther south when the snows of winter, 
cover their food. Most Arctic animals are white or dull 
in color and are provided with thick fur, hair, or feathers 
to protect them from cold. 

The Temperate Realm may be divided into North Amer- 
ica, Eurasian, and Australian regions. It is known that 
many species of animals in the northern temperate regions 
were destroyed by the cold of the glacial period. Several 
species of bears are still found, of which the grizzly is the 



146 



PHYSICAL GEOGRAPHY 



largest and fiercest. Of the great herds of bison that once 
roamed over the western plains, but only a few are now left. 
Mountain lions and big-horn sheep are found in the Rocky 
mountains, and many valuable fur-bearing animals, as 
the otter, mink, beaver, lynx, ermine, sable, and fox are 




Fig. 120. The Bactrian camel. 

found in the Hudson Bay region. Horses, cattle, deer, 
and antelope are native to the central plain. 

The Eurasian Realm includes Europe, northern Asia, 
and northern Africa. Among beasts of burden are the 
yak, camel, dromedary, the wild horse, and ass. The 
yak Is found only on the high plateaus. It is domesticated 
as well as wild, and supplies milk, meat, and valuable 



ANIMAL LIFE 



147 




Fig. 121. Armadillo. 



skins as well as useful labor. The chamois is another 
peculiar mountain animals; it is found among the rocky 
heights of the Alps. Many birds and animals are common 
to the whole northern realm of America, Europe and 
Asia. Crows, finches, grouse, jays, pheasants, bears, 
deer, antelope, wolves, frogs, mice, moles, rats, and count- 
less other varieties 
are found only in 
the northern 
region. 

The Australian 
Realm is the most 
remarkable of all 
the plant and vege- 
table regions. It 
is difficult to find 
there any forms that occur in the other continents. The 
Australian realm includes also New Zealand, New Guinea, 
Tasmania and the neighboring islands. The marsupials, 
or pouched animals, are found here; they have a fold in the 
skin on the under side of the body, in which the young 
are carried while helpless. These animals progress by 
hopping on their hind legs, aided by a long muscular tail. 
The kangaroo is the leading species of them. The emu 
and cassowary are birds without wings; they have hair 
instead of feathers and can run very fast. The lyre- 
bird, the cocatoo, the kiwi, the parrots, and the apteryx 
of New Zealand are entirely unlike any other birds. Many 
animals like those of the Australian kingdom are found in 
the rock layers of Eurasia; but the only living specimen 
that resembles them is the opossum of the United States. 
It is believed that Australia was once connected with the 



148 PHYSICAL GEOGRAPHY 

mainland of Eurasia, and that these animals were common 
to both regions; but the larger and fiercer Eurasian animals 
lived at that time far to the north and did not find their 
way to the Australian region. Afterward, by a sinking 
of the land, a deep-sea passage was formed between the 
two continents. Being thus cut off from the fierce enemies 




that destroyed their Eurasian relatives, the peculiar 
animals of Australia have lived In peace down to the 
present to show us some of the strange creatures that 
were once widely spread over other lands. 

The South American Reahn has some animals quite 
as strange as those of Australia. The condor, the largest 
bird of flight, lives among the Andes, The rhea, or Amer- 
ican ostrich, is found upon the plains, the grass of which 
it resembles in color. South America is the home of bright- 
colored birds. Parrots, tanagers, the toucan, the umbrella- 
bird, and almost 400 species of hummingbirds are found. 
They are red, yellow, bright green, orange — as bright in 



ANIMAL LIFE 



149 



color as the flowers among which they flit. Monkeys, 
serpents, and insects are quite as plentiful as birds. The 
shields of bright-colored beetles and the feathers of birds 
are used by the Indian in making ornamental work remark- 
able for beauty. The jaguar, a kind of panther, is the 
only dangerous wild animal. It prowls about at night, and 




Fig. 123. The apterlx. 

sometimes enters the cabins of natives. The llama, 
alpaca, vicuna, chinchilla, and the guanaco are animals 
of the camel family, but are very much smaller. Their 
fine hair is valuable for making cloth. South America 
affords splendid pastures for horses, cattle, and sheep, 
but none is native to the country, having all been taken 
there by settlers. 

The African Realm is the most famous for animals of 
great size, fierceness, and strength. The elephant, leop- 



ISO 



PHYSICAL GEOGRAPHY 



ard, lion, rhinoceros, hippopotamus, gorilla, and wild 
boar are most familiar. The hyena, quagga, the horned 
gnu, many species of deer, as the eland, giraife and antelope 
also abound. The chimpanzee is the animal that most 
resembles man. The most famous bird is the ostrich, 




Pig. 124. The emu. 

which is hunted and domesticated for its beautiful feathers. 
A curious insect is the tsetse fly, which lives within a limited 
area, and whose sting is fatal to cattle, horses, and dogs, 
but does not injure man. 

The Oriental Realm includes southern Asia and the 
East India islands. The elephant, the zebra, and the 
water buffalo are the most useful animals found in this 
region, and are trained to do all manner of work. The 
rhinoceros, tiger, and lion are also found. The animals 
are most like those of Africa. The man-like apes, the 



ANIMAL LIFE 



151 



orang, and the gibbon resemble the chimpanzee and the 
gorilla. Poisonous serpents are common. The Indian 
cobra is the most dangerous of these. Huge crocodiles 
are found in the Ganges delta and are useful to man in 




Fig. 125. The sun bear of the Oriental realm. 

consuming the carrion that floats down stream. The 
fauna (animal life) of the islands resembles that of the 
continent except that none of the larger and fiercer animals 
are found. 

The ocean everywhere teems with life. Its shallow 



152 



PHYSICAL GEOGRAPHY 




Fig. 126. The orang. 

rocks. Others, as the crabs and 

bottom. The seal and walrus 

being partly 

land animals. 

They with the 

whale and 

dolphin are 

mammals, and 

suckle their 

young. Curious 

animals have 

been brought up 

from the ocean 

bottom by 

dredging. Some 

of these are 

blind. Others 

give out a phos- 

phorescentlight, 

resembling in 



waters are filled with 
many varieties of fish, 
whose names are well- 
known to all on ac- 
count of their value 
as food. Many sea- 
animals resemble 
plants in lacking the 
power of locomotion. 
Sponges, polyps, barn- 
acles, and sea anem- 
ones are fixed to the 
lobsters, crawl upon the 
have been mentioned as 




The chimpanzee. 



ANIMAL LIFE 



153 



this particular certain minute forms that float on the surface 
of the ocean and emit a faint glow. The animals found 
in the greatest abundance and variety are shellfish. They 
take the lime from the water and build up their shells. 
Their shells are washed upon the shore or sink to the bottom 




Frg. 128. Forms of marine life. At the top are corals with polyps, a sword-fish and 
jelly-fish. Several curious fishes found in tropical seas are in the center. At the bottom, 
are sea anemones and a star-fish. 

in shallow waters. Such lime deposits, when raised up 
into hills and mountains, form a large part of the rocks 
of the earth's crust (page 36). 

REVIEW. I. Differences between plants and animals. 2. Show how animals are 
adapted to their surroundings. 3. How are animals fitted for obtaining food.? How for 
defense? 4. What is said of extinct animal life? 5. Name animals which have recently 
become extinct or are in danger of becoming so. 6. What is meant by "survival of the 
fittest''? 7. Explain why some animals are more widely distributed than others. 8. 
Name the three zones of animal life. 9. What are the three divisions of the temperate 
realm? 10. Name the characteristic animals of Eurasia; of North America; of Australia. 
II. Describe the animals of the South American realm. 12. Animals of the y\frican 
realm. 13. Animals of the Oriental realm. 14. Describe the animal life of the ocean. 



CHAPTER XXI 

MAN 

Origin of Man. How and where man first appeared 
upon the earth we do not know. As to when he appeared, 
we can only say that there is good proof that he was on 
the earth at the time of the glacial period, and that this 
was many thousands of years ago. He did not appear 
until the earth was fitted to support human life. In the 
earliest period of the earth's history there was only dead 
matter. But when the waters cooled, plant and animal 
life appeared in the sea; and when the land rose above 
the waters and soil formed, it appeared also upon the 
land. At first only the lowest forms of life are found — 
seaweeds, lichens, and mosses among plants, and shell- 
fish, polyps, worms, and articulates among animals. But 
as ages passed, the forms of plants and animals became 
more elaborate. Fishes, reptiles, mammals, and man 
appear in a constantly ascending series. 

Evolution. In the case of plants and the lower animals 
it is clear that higher forms come as the result of improved 
environment, or surroundings. These consist of better 
air, light, and food. If we cultivate a wild plant, or tame 
a wild animal, we obtain after a few generations better 
varieties and breeds. This obtaining of higher forms out 
of lower ones is called evolution or development. 

Some people believe also that man is a development 
from lower forms of animal life, such as the ape, the gorilla, 
or the monkey. This theory, however, is not proved. 

IS4 



MAN 



155 



All the knowledge we have concerning these matters is 
obtained from the study of the fossils, or remains of living 
things found in rocks. No living or dead species of an- 
imals have yet been found which resemble man closely 
enough to make us believe that he is descended from 




Fig. 129. Homes in New Guinea. 

them. There is too great a difference in the shape and 
capacity of the skull to permit the belief that one descended 
from the others. 

The great and distinguishing feature of man is the posses- 
sion of language, or articulate speech, while animals have 
only a cry, a continuous sound. Man also has reason, 
which is power to distinguish right and wrong, true and 
false, good and evil. This power no animal possesses. 

Civilization. But the quality that makes the greater 



1^6 



PHYSICAL GEOGRAPHY 



gulf between man and the animals Is his capacity for 
improvement. It is true that some tribes and nations 
remain stationary in the savage or partly civilized state. 
But it is also true that they show the ability to improve 
their condition when the way is pointed out to them. 

It is beyond doubt that in 
his original condition man 
was a savage. He lived in a 
thicket or a cave; he was un- 
clothed, and his food was the 
fruit of the earth and such 
animals as he could kill with 
his hands. The use of fire 
and the making of knives, 
axes, and spear-heads from 
stone were among his earliest 
inventions. The invention of 
the bow and the making of 
pottery were the next great 
steps in advance. The game 
that he killed with his arrow 
supplied food, clothing and 
shelter. The vessels of clay 
could be used for cooking and 
storing his food and drink. The discovery of fire led to 
the working of metals and to improvement in the weapons 
and implements that man used. The taming of the cow, 
sheep, goat, horse, and camel was the next advance. Man 
became a shepherd and herdsman. At about the same 
time the cultivation of food-plants was begun. Fruits and 
grains are still the chief food of mankind. 

Commerce is man's natural impulse; trade began as 




Fig. 130. 
America. 



Native Indian of Central 



MAN 



157 




Fig. 131. Civilized life — country. 




Fig. 132. Civilized life — city. 



158 



PHYSICAL GEOGRAPHY 



soon as a man had acquired something that he did not 
need and had found another man with something that he 
did need. Trade promotes industry, and is a great civiHz- 
ing agent. Men learn from each other; the need of keep- 
ing accounts led to a 
system of writing. The 
Phenicians, the great 
commercial nation of 
ancient time, invented 
the alaphabet and 
carried it to every part 
of the known world. 
Manufacturing is en- 
couraged by trade. 
Men make those things 
which they need for 
themselves and also the 
things which they can 
sell to others. Trade 
and manufacturing led 
to the discovery of new 

Fig. 133. Chinese official. J^^^^g ^^^ ^^^ planting 

of colonies. New supplies of raw material must be found 
and new markets for the manufactured products. 

Stages of Progress. On the basis of occupation we 
may divide mankind into five classes: hunters, herdsman, 
farmers, manufacturers, and merchants. We may also 
divide them according to the materials and forces employed. 
Thus we have the age of stone, the age of bronze, the age 
of iron, and the age of steel. We also speak of the age 
of steam and the age of electricity. All these stages 
indicate the gradual civilization of man. 




MAN 



159 



Distribution of Man. Every part of the world that 
supplies food and sufficient protection from the elements 
is inhabited by man. And the earliest mention we have 
of any land shows that it was then an inhabited land. 
Wherever explorers and colonists have gone, some earlier 
race is found in possession of the soil. The reason for 
this wide dis- 
tribution of 
man is that he 
is able to over- 
come the disad- 
vantages of 
climate. His 
intelligence en- 
ables him to 
protect himself 
from heat, 
storm, and cold, 
and to obtain 
food in ways 
impossible to 
the lower animals. It has also enabled him to cross wide 
oceans and thus to pass from continent to continent and 
from island to island until all parts of the habitable have 
become populated by the several races. 

Influence of Climate and Surface. The state of civiliza- 
tion and the occupations of men depend largely upon their 
surroundings. The Eskimos can obtain food and shelter 
sufficient to keep them alive; but the effort to do this takes 
all their time and strength. Among mountam regions, 
too, it is often so difficult to get a living that there is no 
energy left for progress. In the very hot regions of the 




Fig. 134. Natives of New Guinea. 



lOo 



PHYSICAL GEOGRAPHY 



earth, great exertion is neither necessary nor possible. 
Men can live on the natural products of the earth, and 
clothing and shelter are scarcely needed. 

Inland regions are not favorable to civilization, unless 
there is means of intercourse with other people. People 




Fig. 135. A Blackfoot Indian chief. (After Catlin.) 

living remote from the sea coast and having little com- 
munication with the world soon get behind the times in 
language and customs. They do not invent new ways 
of doing things, and they stagnate in both intelligence 
and energy. The best condition for civilization is a land 
where food is abundant and climate temperate, and where 



MAN 



•i6i 



there is good means 

of communication and 

an extensive sea coast. 

Races of Mankind. 

There are several ways 
of classifying man, 
none of which is en- 
tirely satisfactory. 
Men are found of all 
shades of color from 
white to black, and of 
all degrees of civiliz- 
ation. Different sur- 
roundings after long 
periods of time pro- 
duce different races. 
It is believed that all 
mankind are descended 










0k^^i 


W! ■ 










f jy^M** 


i 


m^M 


l^'ohL 




W-^^^^w 


j^H 


Bi 


i^^eshh 


-'^WM^ 


^ 


Hni 


HH 


u^^M 


H 


Hp^ 


R^H 




mM^ 




iXMI 


■HI 











Fig. 137. Caucasian race of Western Asia. 



Fig. 136. Hindoos. 

from one pair and that the varied 
races of the 
earth are the 
result of physi- 
cal surround- 
i n g 8 and 
different modes 
of life. How 
long a time 
must have 
elapsed, then, 
between the 
creation of our 
first parents 
andthepresent! 



l62 



PHYSICAL GEOGRAPHY 



Each nation develops a slight variation in race. The 
English, Dutch, and Germans are of the same race, and 
once lived on the same soil. But it is easy now to dis- 
tinguish them. 

According to color features, we may divide mankind into 
four distinct races: the white, yellow, red, and black. 

Woolly hair, thick lips, flat 
nose, black eyes, and low 
civilization characterize the 
black races of Africa and the 
islands of the Pacific ocean. 
The Mongolian, or yellow, 
races have a color ranging 
from yellow to brown, small, 
black eyes obliquely set, and 
straight, black hair. In 
civilization they range from 
the highest to the lowest. 
The American, or red, race 
is marked by straight, black 
hair, straight nose, black 
eyes, and low rank in civiliz- 
ation. The Caucasian is the 
highest type of mankind. In 
complexion and in color of 

Fig. 138. A Manchu lady. J^^j^. ^^^ ^^^g ^^^ mcmbcrS of 

this race vary. Their features are regular, with straight 
nose, thin lips, and wavy and abundant hair and beard. 
They rank highest in civilization, and are especially noted 
for their inventive genius, manufacturing skill and attain- 
ments in the fine arts and literature. 

The white races are noted for the control they have 




MAN 



163 



obtained over the resources of the earth by improved meth- 
ods in agriculture, mining, natural power, and transportation. 
Steam, water power, and electricity are utilized according 
as economy or 
commerce dic- 
tates. Enter- 
prise, wealth, 
and steamship 
navigation have 
carried them 
into every part 
of the globe, 
while the other 
have 



races 



re- 



mained station- 
ary or have de- 
clined in power. 




Fig. 139. Arabs at prayer. 



REVIEW. I. What is said of the origin of man.? 2. Tell something about the 
succession of life which has appeared upon the earth. 3. What is meant by evolution? 
4. What objection is there to the theory that man has been evolved from lower animal 
forms? 5. Name the several stages of progress or civilization characteristic of man. 
6. Distribution of man. 7. How is civilization affected by surface and climate? 8. What 
are the three leading races of mankind? 



INDEX 



Agate, 40 
Air Plants, 137 
Amazon River, "]'] 
Amethyst, 40 
Animals, 140-153 
Antarctica, 42 
Anticyclone, 119 
Aphelion, 4 
Artesian Wells, 76-77 
Asteroids, 2 
Atmosphere, 34, 42, 99 
Atoll, 80, 82 
Avalanches, 50 
Axis, 17, 19 

B 

Barometer, loo-ioi 
Blizzard, 120 
Block Structure, 45 
Bluestone, 35 
Bore, 95 
Boulder, 68 
Breakers, 91-92 
Buttes, 48 



Carbon, 39, 40 
Carbon Dioxide, 99, 134 
Casco Bay, 79 
Caverns, 66 
Centrosphere, 34 
Chinooks, 125 
Civilization, 155-156 
Clay, 39 
Climate, 124 
Clouds, 102-104 
-106 Coast Line, 82-87 

Coast Survey, U. S,, 84 
Compass, 26 
Commerce, 156-157 
Comets, 5, 6 
Conglomerate, 35 
Constant Winds, 114 
Constellations, i 
Continental Islands, 79-81 
Continents, 41-43 
Corpernicus, 6 
Coral Islands, 81-83 
Crystalline Rock, 37, 38 
Currents, Ocean, 95-98 
Cyclones, 11 8-1 19 
164 



INDEX 



i6q 



D 
Day, i8, 19 
Declination, 22, 27, 28 
Deltas, 64 
Dew, 104-105 
Dikes, 4.7 
Dip, 22 

Dipping Needle, 27 
Direction, 15 
Distributaries, 65 
Drainage, 73 

E 

Earth, 3, 7, 11-13 
Earthquakes, 55-57 
Eccentricity, 4 
Eclipse, 12; of moon, 32; of 

sun, 33 
Elevation, 125 
Ellipse, 4 
Equinoxes, 16, 17 
Erosion, 59 
Estuary, 85 
Evolution, 154 



Fault, 44-45 
Feldspar, 39 
Fiords, 86 
Firths, 86 
Fishing Banks, 68 
Fixed Stars, 2 



Floes, 98 
Foci, 4 
Fog, 102 
Fold, 45 
Fossils, 36, 155 
Foehn (fohn), 129 
Foucault (fooko), 14, 15 
Frost, 104-105 



Gems, 40 
Geysers, 57-58 
Glacial Drift, 68-69 
Glacial Lakes, 70, 75 
Glaciers, 66-71 
Gneiss, 37 
Gobi Desert, 76 
Gradient, no 
Granite, 37 
Gravel, 39 
Gravitation, 9, 93 
Great Bear, i 
Great Plains, 48 
Greenwich, 20 

H 

Hail, 104 

Halley, Edmund, 6 

Hawaii, 53 

Heat Belts, 107 

Herculaneum, 54, 55 

Hercules, i 



1 66 

Hook, 87 
Hot Springs, 57 
Humidity, 102 
Hurricane, 121 
Hyades, i 
Hydrosphere, 34, 40-41 



Icebergs, 68, 89, 98 
Igneous Rock, 37, 41 
Inertia, 9 

Intermittent Springs, 77 
International Date Line, 

24-25 
Islands, 79-83 
Isobars, no 
Isotherms, 108 



Jupiter, 2, 3, 5, 7, 8 

K 

Kepler, Johann, 3 
Khaibar Pass, 49 
Krakatoa, 54 



Lakes, 75 
Landslides, 50, 51 
Latitude, 20-23 
Lava, 37, 52-53 



INDEX 



\ 



Lightning, 123 
Lime, 39 
Limestone, 35 
Lithosphere, 34 
Local Time, 23 
Location, 20 
Longitude, 20-23 
Luray Caverns, 66 

M 

Magnetic Meridian, 27 
Magnetic needle, 26-27 
Magnetism, 26, 28, 29 
Mammoth Cave, 66 
Man, 134-163 
Mantle Rock, 38 
Marble, 37 
Mari, 39, 40 
Mars, 2, 3 
Martinique, 54 
Mauna Loa, 53 
Mercury, 2, 3 
Meridians, 20 
Mesas, 48 
Metals, 39 
Meteors, 5, 6 

Metamorphic Rock, 37, 38 
Mica, 39 
Minerals, 39, 40 
Mississippi River, 63, 74 
Mist, 102 
Monsoons, 114 



INDEX 



167 



Mont Pelee, 54 
Mo..n, 5, 30-31 
Moraines, 67 
Mountains, 44-46 

N 

Nebular Theory, 7, 8 
Neptune, 2, 3 
Newton, Sir, Isaac, 9 
Night, 18, 19 
Nitrogen, 99 
North Star, i 
Notre Dame, 15 

O 

Ocean Life, 151 

Onyx, 40 

Opal, 40 

Oxygen, 42, 60-61, 99, 133 



Pleiades, i 
Polaris, i 
Polyps, 82 
Pompeii, 54, 55 
Pressure, 89, 108 



Quartz, 39 



R 



Races, 95, 161-163 
Railroad Time, (See Stand- 
ard Time) 
Rain, 104 
Rainbow, 123 
Rainfall, 115, 118 
Reefs, 82 
Revolution, 14-18 
Rotation, 14-15 



Parallels, 20, 21 
Parasites, 137 
Passes, 49-50 
Peat, 39 
Peneplain, 46 
Perihelion, 4 
Periodic Winds, 114 
Planets, 2, 7, 8 
Plant Life, 131-139 
Plateaus, 44-46, 47-48 



St. Pierre, 54 
Salt Lakes, 75-76 
Sand, 39, 40 
Sand Dunes, 62 
Sandstone, 35 
Saturn, 2, 3, 7, 8 
Sea, 88 
Sea Level, 88 
Seasons, 15-19 
Sextant, 22 
Shale, 35 



1 68 



INDEX 



Silica, 40 
Sirius, I 
Slate, 35 
Snow, 104 

Solar System, 6, 7, 8 
Solstices, 16, 18 
Spheroid, 13 
Spit, 87 
Springs, 76 
Stacks, 86 
Stalagmite, 65, 66 
Stalactite, 65, 66 
Standard Time, 23 
Stratified Rock, 34-36 
Storm Charts, 122 
Storms, 1 1 8-1 19 
Stromboli, 53 
Sun, 6, 8, 17-19 
Surf, 92-91 



Talus, 61 

Thermometer, loi, 102 
Thunderstorms, 122 
Tides, 92-95 
Time Belts, 23 
Tornado, 120 
Trade Winds, 114 



Typhoon, 121 
Twins, I 



U 



Uranus, 3, 7 



Valleys, 64 
Venus, 3, 7 
Vesuvius, 54, 55 
Volcanic Islands, 81 
Volcanic Rock, (see Igneous 

Rock) 
Volcanoes, 52-55 

W 

Watersheds, 74 
Waterspout, 121 
Waves, 90-91 
Weather, 124 
Weather Bureau, 127-128 
Weathering, 60 
Weather Maps, 128-129 
Weight, 9 
Wells, 76 
Winds, 111-115 

Z 

Zenith Distance, 22 



UN /^3 IHIiJ 






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